I tested an app for Android devices. Really good (BedTimeNow)
you put off time and on time, then activate. Then you forget about it. The tablet locks each night and opens each morning (for me it's 8.30 pm lock and open at 7.30 am) so no arguments with the kids about turning the tablet off when going to bed
if you need the device you can unlock it
check it out, download for free