For the 9:30 am tour, how early should I arrive to have enough time to check in and board?

Maybe 30-40 minutes early you should be fine.

30 mins should be good. First comers get best seats.. but I see, most people didn't bother, because as the tour starts everyone gets up and start taking pictures..

30 min early would be fine, you can look around , also when you are in front of line, you can get a better spot

30 -20 minutes is good

I was thirty minutes early on a Thursday and had plenty of time to walk around the oceanfront and take in some sights before boarding.

Generally if you are 30 mins to 45 mins early you should be fine. The line gets long closer to boarding time. The closer to the front of the line, the better seats you can pick!