I'd say get there around 8am. Last time I got there at 7:45 and by 8:15 the line was full. (considering they give 50 tix per show, a LOT of ppl showed up in 30 min)
Sundays you can get there a little later as the box office opens at 12. I got there last Sunday at 9 and was good but it was full by 930 I would guess. Also it did not fill up this morning until a little later being that it was really cold, but evening tickets go faster so...