diff --git a/src/action/addusedtime2.ts b/src/action/addusedtime2.ts
new file mode 100644
index 0000000..9c456f5
--- /dev/null
+++ b/src/action/addusedtime2.ts
@@ -0,0 +1,98 @@
+/*
+ * server component for the TimeLimit App
+ * Copyright (C) 2019 - 2020 Jonas Lochmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import { uniq } from 'lodash'
+import { assertIdWithinFamily } from '../util/token'
+import { AppLogicAction } from './basetypes'
+
+export class AddUsedTimeActionVersion2 extends AppLogicAction {
+  readonly dayOfEpoch: number
+  readonly items: Array<{
+    readonly categoryId: string
+    readonly timeToAdd: number
+    readonly extraTimeToSubtract: number
+  }>
+
+  constructor ({ dayOfEpoch, items }: {
+    dayOfEpoch: number
+    items: Array<{
+      categoryId: string
+      timeToAdd: number
+      extraTimeToSubtract: number
+    }>
+  }) {
+    super()
+
+    if (dayOfEpoch < 0 || (!Number.isSafeInteger(dayOfEpoch))) {
+      throw new Error('illegal dayOfEpoch')
+    }
+
+    if (items.length === 0) {
+      throw new Error('missing items')
+    }
+
+    if (items.length !== uniq(items.map((item) => item.categoryId)).length) {
+      throw new Error('duplicate category ids')
+    }
+
+    items.forEach((item) => {
+      assertIdWithinFamily(item.categoryId)
+
+      if (item.timeToAdd < 0 || (!Number.isSafeInteger(item.timeToAdd))) {
+        throw new Error('illegal timeToAdd')
+      }
+
+      if (item.extraTimeToSubtract < 0 || (!Number.isSafeInteger(item.extraTimeToSubtract))) {
+        throw new Error('illegal extra time to subtract')
+      }
+    })
+
+    this.dayOfEpoch = dayOfEpoch
+    this.items = items
+  }
+
+  serialize = (): SerializedAddUsedTimeActionVersion2 => ({
+    type: 'ADD_USED_TIME_V2',
+    d: this.dayOfEpoch,
+    i: this.items.map((item) => ({
+      categoryId: item.categoryId,
+      tta: item.timeToAdd,
+      etts: item.extraTimeToSubtract
+    }))
+  })
+
+  static parse = ({ d, i }: SerializedAddUsedTimeActionVersion2) => (
+    new AddUsedTimeActionVersion2({
+      dayOfEpoch: d,
+      items: i.map((item) => ({
+        categoryId: item.categoryId,
+        timeToAdd: item.tta,
+        extraTimeToSubtract: item.etts
+      }))
+    })
+  )
+}
+
+export interface SerializedAddUsedTimeActionVersion2 {
+  type: 'ADD_USED_TIME_V2'
+  d: number
+  i: Array<{
+    categoryId: string
+    tta: number
+    etts: number
+  }>
+}
diff --git a/src/action/index.ts b/src/action/index.ts
index 3a0e707..def6420 100644
--- a/src/action/index.ts
+++ b/src/action/index.ts
@@ -21,6 +21,7 @@ export { AddCategoryAppsAction } from './addcategoryapps'
 export { AddUserAction } from './adduser'
 export { AddInstalledAppsAction } from './addinstalledapps'
 export { AddUsedTimeAction } from './addusedtime'
+export { AddUsedTimeActionVersion2 } from './addusedtime2'
 export { ChangeParentPasswordAction } from './changeparentpassword'
 export { ChildChangePasswordAction } from './childchangepassword'
 export { ChildSignInAction } from './childsignin'
diff --git a/src/action/serialization/applogicaction.ts b/src/action/serialization/applogicaction.ts
index 0a514af..eb87bf0 100644
--- a/src/action/serialization/applogicaction.ts
+++ b/src/action/serialization/applogicaction.ts
@@ -1,6 +1,6 @@
 /*
  * server component for the TimeLimit App
- * Copyright (C) 2019 Jonas Lochmann
+ * Copyright (C) 2019 - 2020 Jonas Lochmann
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
@@ -17,6 +17,7 @@
 
 import { AddInstalledAppsAction, SerializedAddInstalledAppsAction } from '../addinstalledapps'
 import { AddUsedTimeAction, SerializedAddUsedTimeAction } from '../addusedtime'
+import { AddUsedTimeActionVersion2, SerializedAddUsedTimeActionVersion2 } from '../addusedtime2'
 import { AppLogicAction } from '../basetypes'
 import { RemoveInstalledAppsAction, SerializedRemoveInstalledAppsAction } from '../removeinstalledapps'
 import { SerializedSignOutAtDeviceAction, SignOutAtDeviceAction } from '../signoutatdevice'
@@ -27,6 +28,7 @@ import { SerializedUpdateDeviceStatusAction, UpdateDeviceStatusAction } from '..
 export type SerializedAppLogicAction =
   SerializedAddInstalledAppsAction |
   SerializedAddUsedTimeAction |
+  SerializedAddUsedTimeActionVersion2 |
   SerializedRemoveInstalledAppsAction |
   SerializedSignOutAtDeviceAction |
   SerialiezdTriedDisablingDeviceAdminAction |
@@ -36,6 +38,8 @@ export type SerializedAppLogicAction =
 export const parseAppLogicAction = (serialized: SerializedAppLogicAction): AppLogicAction => {
   if (serialized.type === 'ADD_USED_TIME') {
     return AddUsedTimeAction.parse(serialized)
+  } else if (serialized.type === 'ADD_USED_TIME_V2') {
+    return AddUsedTimeActionVersion2.parse(serialized)
   } else if (serialized.type === 'ADD_INSTALLED_APPS') {
     return AddInstalledAppsAction.parse(serialized)
   } else if (serialized.type === 'REMOVE_INSTALLED_APPS') {
diff --git a/src/api/validator.ts b/src/api/validator.ts
index 7959c61..354258a 100644
--- a/src/api/validator.ts
+++ b/src/api/validator.ts
@@ -1152,6 +1152,49 @@ const definitions = {
       "type"
     ]
   },
+  "SerializedAddUsedTimeActionVersion2": {
+    "type": "object",
+    "properties": {
+      "type": {
+        "type": "string",
+        "enum": [
+          "ADD_USED_TIME_V2"
+        ]
+      },
+      "d": {
+        "type": "number"
+      },
+      "i": {
+        "type": "array",
+        "items": {
+          "type": "object",
+          "properties": {
+            "categoryId": {
+              "type": "string"
+            },
+            "tta": {
+              "type": "number"
+            },
+            "etts": {
+              "type": "number"
+            }
+          },
+          "additionalProperties": false,
+          "required": [
+            "categoryId",
+            "etts",
+            "tta"
+          ]
+        }
+      }
+    },
+    "additionalProperties": false,
+    "required": [
+      "d",
+      "i",
+      "type"
+    ]
+  },
   "SerializedRemoveInstalledAppsAction": {
     "type": "object",
     "properties": {
@@ -1692,6 +1735,9 @@ export const isSerializedAppLogicAction: (value: object) => value is SerializedA
     {
       "$ref": "#/definitions/SerializedAddUsedTimeAction"
     },
+    {
+      "$ref": "#/definitions/SerializedAddUsedTimeActionVersion2"
+    },
     {
       "$ref": "#/definitions/SerializedRemoveInstalledAppsAction"
     },
diff --git a/src/function/sync/apply-actions/cache.ts b/src/function/sync/apply-actions/cache.ts
index a38317d..f9ae4d9 100644
--- a/src/function/sync/apply-actions/cache.ts
+++ b/src/function/sync/apply-actions/cache.ts
@@ -120,7 +120,7 @@ export class Cache {
   })
 
   shouldDoFullSync = () => this.shouldTriggerFullSync
-  requireFullSync = () => this.shouldTriggerFullSync = true
+  requireFullSync: () => void = () => this.shouldTriggerFullSync = true
 
   async saveModifiedVersionNumbers () {
     const { database, transaction, familyId } = this
diff --git a/src/function/sync/apply-actions/dispatch-app-logic-action/addusedtime.ts b/src/function/sync/apply-actions/dispatch-app-logic-action/addusedtime.ts
index bf8cd7f..a259f21 100644
--- a/src/function/sync/apply-actions/dispatch-app-logic-action/addusedtime.ts
+++ b/src/function/sync/apply-actions/dispatch-app-logic-action/addusedtime.ts
@@ -19,7 +19,7 @@ import * as Sequelize from 'sequelize'
 import { AddUsedTimeAction } from '../../../../action'
 import { Cache } from '../cache'
 
-const getRoundedTimestamp = () => {
+export const getRoundedTimestamp = () => {
   const now = Date.now()
 
   return now - (now % (1000 * 60 * 60 * 24 * 2 /* 2 days */))
diff --git a/src/function/sync/apply-actions/dispatch-app-logic-action/addusedtime2.ts b/src/function/sync/apply-actions/dispatch-app-logic-action/addusedtime2.ts
new file mode 100644
index 0000000..04d8742
--- /dev/null
+++ b/src/function/sync/apply-actions/dispatch-app-logic-action/addusedtime2.ts
@@ -0,0 +1,100 @@
+/*
+ * server component for the TimeLimit App
+ * Copyright (C) 2019 - 2020 Jonas Lochmann
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import * as Sequelize from 'sequelize'
+import { AddUsedTimeActionVersion2 } from '../../../../action'
+import { Cache } from '../cache'
+import { getRoundedTimestamp } from './addusedtime'
+
+export async function dispatchAddUsedTimeVersion2 ({ deviceId, action, cache }: {
+  deviceId: string
+  action: AddUsedTimeActionVersion2
+  cache: Cache
+}) {
+  const roundedTimestamp = getRoundedTimestamp().toString(10)
+
+  for (let i = 0; i < action.items.length; i++) {
+    const item = action.items[i]
+
+    const categoryEntryUnsafe = await cache.database.category.findOne({
+      where: {
+        familyId: cache.familyId,
+        categoryId: item.categoryId
+      },
+      transaction: cache.transaction,
+      attributes: [
+        'childId',
+        'extraTimeInMillis'
+      ]
+    })
+    // verify that the category exists
+    if (!categoryEntryUnsafe) {
+      cache.requireFullSync()
+
+      return
+    }
+
+    const categoryEntry = {
+      childId: categoryEntryUnsafe.childId,
+      extraTimeInMillis: categoryEntryUnsafe.extraTimeInMillis
+    }
+
+    if (item.timeToAdd !== 0) {
+      // try to update first
+      const [updatedRows] = await cache.database.usedTime.update({
+        usedTime: Sequelize.literal(`usedTime + ${item.timeToAdd}`) as any,
+        lastUpdate: roundedTimestamp
+      }, {
+        where: {
+          familyId: cache.familyId,
+          categoryId: item.categoryId,
+          dayOfEpoch: action.dayOfEpoch
+        },
+        transaction: cache.transaction
+      })
+
+      // otherwise create
+      if (updatedRows === 0) {
+        await cache.database.usedTime.create({
+          familyId: cache.familyId,
+          categoryId: item.categoryId,
+          dayOfEpoch: action.dayOfEpoch,
+          usedTime: item.timeToAdd,
+          lastUpdate: roundedTimestamp
+        }, {
+          transaction: cache.transaction
+        })
+      }
+
+      cache.categoriesWithModifiedUsedTimes.push(item.categoryId)
+    }
+
+    if (item.extraTimeToSubtract !== 0) {
+      await cache.database.category.update({
+        extraTimeInMillis: Math.max(0, categoryEntry.extraTimeInMillis - item.extraTimeToSubtract)
+      }, {
+        where: {
+          familyId: cache.familyId,
+          categoryId: item.categoryId
+        },
+        transaction: cache.transaction
+      })
+
+      cache.categoriesWithModifiedBaseData.push(item.categoryId)
+    }
+  }
+}
diff --git a/src/function/sync/apply-actions/dispatch-app-logic-action/index.ts b/src/function/sync/apply-actions/dispatch-app-logic-action/index.ts
index 1e7c64a..f91deb3 100644
--- a/src/function/sync/apply-actions/dispatch-app-logic-action/index.ts
+++ b/src/function/sync/apply-actions/dispatch-app-logic-action/index.ts
@@ -1,6 +1,6 @@
 /*
  * server component for the TimeLimit App
- * Copyright (C) 2019 Jonas Lochmann
+ * Copyright (C) 2019 - 2020 Jonas Lochmann
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
@@ -18,6 +18,7 @@
 import {
   AddInstalledAppsAction,
   AddUsedTimeAction,
+  AddUsedTimeActionVersion2,
   AppLogicAction,
   RemoveInstalledAppsAction,
   SignOutAtDeviceAction,
@@ -28,6 +29,7 @@ import {
 import { Cache } from '../cache'
 import { dispatchAddInstalledApps } from './addinstalledapps'
 import { dispatchAddUsedTime } from './addusedtime'
+import { dispatchAddUsedTimeVersion2 } from './addusedtime2'
 import { dispatchRemoveInstalledApps } from './removeinstalledapps'
 import { dispatchSignOutAtDevice } from './signoutatdevice'
 import { dispatchTriedDisablingDeviceAdmin } from './trieddisablingdeviceadmin'
@@ -43,6 +45,8 @@ export const dispatchAppLogicAction = async ({ action, deviceId, cache }: {
     await dispatchAddInstalledApps({ deviceId, action, cache })
   } else if (action instanceof AddUsedTimeAction) {
     await dispatchAddUsedTime({ deviceId, action, cache })
+  } else if (action instanceof AddUsedTimeActionVersion2) {
+    await dispatchAddUsedTimeVersion2({ deviceId, action, cache })
   } else if (action instanceof RemoveInstalledAppsAction) {
     await dispatchRemoveInstalledApps({ deviceId, action, cache })
   } else if (action instanceof SignOutAtDeviceAction) {