We've never had trouble getting chairs in September and October when most kids are in school. We just got back from our trip over the 4th of July holiday and SAB was pretty crowded the whole time, especially on the 4th.
We were having breakfast at the Captain's Grille on our last morning, July 5th and we were sitting by a window near the entrance to SAB. We sat down at 8:45am and there were already people waiting in line to get their favorite spots in SAB. They grabbed their tables and laid towels over multiple chairs. I assume they were taking one for each of their family members, although, none of the family members were there, of course. For the most part, the person who came early to get their favorite spots stayed there. And it was really hard to tell who was at the pool, in the water, and who wasn't.
We went back to our room after breakfast to pack and check our bags with the airline bag service before heading to the pool. We got to SAB around 10:40am and there were still some tables left in the shade, but I would say they were all filled up by 11am. It wasn't too hard to find a single chair to lay your stuff on, but it would have been hard to find a group of chairs together if you came in after noon. I guess summer is a popular time for SAB, because we've never seen it fill up like this during the school year. We spent two afternoons at the quiet pool and there were very few people there.
I timed the bus ride from BC to AK and it was about 15 minutes long. I was surprised at how fast the trip was.
We went there for dinner one night and they have a lot of food options there. Then we got on the boat to DHS after dinner. It was very convenient.