I have boarded my baby for up to 5 days she was fine, the initial day took an adjustment but afterwards she did well. I think she handled it better than I did!
Beyond the time, what is important is the environment, I would visit several different places first as all boarding facilities are not equal!!! Also compare the activities they have available - do they offer regular play time, do they keep small dogs segregated from larger dogs, are the dogs in their own area or is it a wide open space? I've seen both and I don't like the thought of my 4 pound yorkie in an open space with dogs that are 10 and 12 pounds! The facility I use have a puppy room where small adult dogs like my yorkie are kept with puppies. Each dog has their own "room" with plenty of space to move about in. They also have several playtime thru out the day.