Time restrictions on users' accounts

[Victor Tsaran]

Hello, listers!
I know this is off topic, but knowing how many experienced Linux users are
there on this list, I decided to take a risk!
Where would I look to find the inroamtion on how to put time restrictions on
users' accounts. For instance, say, I would like to log users out if they
stay online for more than two hours. Or, say, I would like to deny users
from loging in more than one time.
I'd be grateful for any suggestions.
Best,
Vic