When DD was 2 years old we kept missing the time for our fast pass for jungle cruise. By time it was ready, she had to leave for nap. We did this twice. We mentioned to the the CM who said
"Let me let you in on a little WDW sercret. The only important time on the fast pass is the start time. Any time after that, even days is fine."
We have used "expired" fast passes many times, no questions ever. I asked once after that and the cast member said, "most of the time they allow it, occasionaly if it is very busy they can't." If that is the case, try it again in a little bit or when there is a different cast member.