I don't exactly agree with Trillian even though it allows you to contact both MSN and AOL chatters. What I don't like is the fact you can't do anything interactive except chat, like games, sending files, etc... bit stupid if you ask me
I don't think there is a setting on MSN to stop it after a couple of hours or so, and you might find it is the version of the program you are using.
Do yuio by any chance use Microsoft Messenger that comes with Windows XP? Or MSN Messenger that you have to download?
Sometimes anyways the connection can be dodgy, since I'm sure everyone gets dissconnections once in a while
Hope this helps