"Check your ticket," my friend said. "The times printed on our tickets are almost over. We won't be able to use them during the time we were planning to meet."
Lo and behold, my husband checked out tickets, and we had the same problem. The thing that really annoyed me is that we'd printed and used our coupons two weeks earlier -- but the time printed on those tickets had been different.
Lesson learned: check your tickets and don't assume the times are the same week to week.