I would be comfortable with clipping and unclipping before going on a group ride. I am a ride leader for a recreational club (i.e. non competitive). I would expect that someone coming on a ride, even a beginner ride would be comfortable with whatever pedal system s/he had, along with shifting, braking, etc. Safety is a major concern on group rides, and in order to enjoy the experience, you should be comfortable. Practice early on a Sunday morning. There's no need to unclip with both feet. Leave your strongest leg clipped in, so you can push off with that one when you start. Make sure you gear down before you stop, so starting again won't be too hard.
I give you credit for riding in a city environment!