I rushed on the 22nd, got there at 6:20 and was the first in line. Second got there at 6:45, third at 7:10, 4th and 5th at around 7:45, and between 7:45 and 8:00, three more people came. Then no one else (that I noticed) until after 8:30–8:40ish, when people started trickling in non-stop. I'd guess it took so long for people to show up since the temperature was below freezing the day I rushed.
A little late to give advice on Sara/Gavin, I know =/ Maybe this'll be applicable if Sara or some other popular actor/actress returns/comes to the diner, lol. I ended up sitting in left orchestra, row C, in the aisle.