In my experience, until a chat room (Be it web based, IRC, et al) gains in popularity, setting a general meeting time helps to encourage it’s use and acceptance. It is of course set as a non-compulsary guideline as others might not be available. Generally the preferred time for many falls in the 9-11PM range EST. As there are areas of the world where this is the middle of the night, or middle of the workday it isn’t perfect for everyone. Just having someone sit in the room encourages more to join. Understand though that if you come into the chat and other users are present but not speaking that they might be in other windows waiting for others (You) to join, but only check back periodically. So be patient at first.
-MJ