We went 2 days in a row (Oct 17 & 18 - a Fri & Sat) and the line was not long on either day. I don't think that many people know about it. And it's really hidden in DCA. You have to know where to go to find it.
You are allowed one print per day, so yes you can go back another day for another shot. We did, and got 2 prints over 2 days. They were both with Daisy.. but, we happened to like both prints and they were free, so can't complain.