A more advanced version of this would be to lock the phone into “emergency calls only” mode within a specific time window. I don’t know how hard that would be to pull off.
The most notable feature lacking is locking the phone when the start time arrives. PM me if you run into problems. Don’t set the end time one minute before the start time, or you’ll only be able to unlock the phone in that minute.
This appears to be possible with the Device Administration API to relock the screen upon receiving an ACTION_USER_PRESENT intent. Neither of which requires a rooted phone.
If you can write an app that kicks the user back to the lock screen within a specific time window, that would be fantastic
Basic version debug apk here, (more recent) source on GitHub, and Google Play.
The most notable feature lacking is locking the phone when the start time arrives. PM me if you run into problems. Don’t set the end time one minute before the start time, or you’ll only be able to unlock the phone in that minute.