If the "Preview new messages" feature is turned on in the Messages app, incoming text messages are displayed in the top notification bar or as a pop-up, allowing you to reply directly from there without opening the Messages app. In this case, messages can be sent even during restricted time periods, and usage time is not calculated correctly. You can resolve this issue as follows.

To prevent the use of the Messages app via the 'Reply' function, configure the settings as shown below.

1) Device 'Settings' menu

2) Applications → Messages app

3) 'Notifications' in application settings