Implement feature not available in Parental Controls?
I'm far too lazy to implement this, and I don't have kids so have no need, but it would seem imminently possible with a cute python or Terminal script set to start running at login. This post seems to go over pretty well the Terminal logout commands. Couple that with the system time, date, is what you'll want and choose whichever output works best for you. Past that, it's somewhat unclear if you should be able to log in as a user again (just put a password on that account with no admin privileges) or if you want to have an admin log a user with no password in. The latter is probably slightly more difficult to do, but assuredly not impossible.