Well, I'm a mod at a baseball related website right now. I noticed you're from NYC, is yours a Yankee or Met related site? If so, which one?
I can tell you from my experience at
www.nyyfans.com that it all depends on the site administrator. The owner/operator of my site is an awesome guy, and makes our jobs as Moderators a lot easier to deal with than they have to be. Also, the committment you're asking about, all depends on what they're asking of you. Jim, the owner/operator i spoke of, didn't ask me for any specific time committment. I just offered what I have. Some of the mod's there aren't even officially listed as mods, even though they do the work.
If you've got a good administrator, and also a good supporting crew of mods around you, it will help your transition into being a mod a lot easier (like asking questions about how to deal with certain situations or certain people).
Overall, it's been a great experience for me, even though it's been tough at times.