Don't worry about them being cooped up for a weekend, they'll be fine. I feel bad too when I go away, but I'd worry more if my dogsitter were faced with chickens going where they're not allowed or flying into the neighbors yard or maybe the dogsitter will forget how important it is to lock them up as soon as the sun goes down and not 1/2 hour later. It might be too daunting for a newbie to get your chickens back in and locked up. If you leave some weeds/clover/lettuce and scratch for them as snacks, especially in the morning it will keep them busy.
