Yep, that’s exactly what I do. I have had a few brides ask me (when they see the overtime clause) what will happen if the ceremony runs long. I tell them not to worry, that my concern is ceremonies which start late. I usually build in about 30 extra minutes (unbeknownst to them) because some officiants are garrulous and because some people think the ceremony begins with the seating of the mothers rather than the processionals. It also doesn’t hurt to let the wedding director know (when you’re setting up) that you will need to leave at x time so she or he can make an attempt to keep things on schedule. It’s really a bummer when you need to leave, they’re late, and the only way out is down the center aisle in front of everybody!