there was no queue at Boston office
I don't think you will be made to wait more than 20-30 minutes, than the time given to you. When you call BCIS and fix the appointment., the rep gives you a confirmation number with the time, the ASC gets that information electronically. When I went to the boston office, the officer verified my name and EAC# against a printed list. So, if you get at the right time, you won't have to wait for a long time. Even, if you have to wait, it is worth waiting, because you can be assured that there won't be any RFE on photos. You might have to wait for the same time in the studio, if you go there for photographs. ASC does the fingerprint, signature and photos within 5 minutes and a supervisor verifies that for quality.
Tammy, i have submitted the renewal about 112 days before its expiry, let us see if this helps the approval of long pending I-140!