Hamsgirl,
My LO loves his playgroup as well! We are lucky enough to be part of a group with babies of many ages. While the older ones play for hours, we younger folks can only stand about an hour max of group time anyway, so we arrive when we can...before or after naps...and stay as long as we can so as not to interrupt naps. DS and I are usually some of the first to arrive, and some of the first to leave. I agree with corrina though...if you do mess with naps one day, do your best to stay on track the nextt day or so, so that you don't create bad habits!