I've done some GMing in the past, mostly 3rd edition, but don't have much experience with 4th. In addition, my schedule's pretty hectic right now, but in the future I might be open to swapping GM duties.
I can probably only commit to twice a month as far as gaming sessions go--I'd like to do more, but with my job / extracurriculars I can't really promise anything beyond that. I live in Central Time, weeknights would work well (except Wednesdays), as well as potentially Friday and Sunday nights and Saturday morning / day.