I did rush for Heathers 3 times when i was there last week, Ive gotten row D, row J, and front row. The time i got front row, i got to the box office right when it opened at 1, so that may have helped. I can almost guarantee you will get seats no matter what time you go.
Tried it yesterday. Got there around 10:15 (opened at 10) and they were sold out of rush tickets for the matinee but still had some left for the 7:30 performance.