The previous poster is correct that you can get multiple FP for the same ride in one day, but I just wanted to add that my understanding is that you can't pull a new FP for the same ride before it's time to use your current FP for that ride, so timing it right to get an evening FP before they run out can be tricky.
So for example if you pull a FP for RSR at 9am and the return time is 2pm, you're eligible for your next FP at 11am, but it has to be for a different ride. You can't pull another RSR FP until 2pm, if they're still available. So the best option to make sure you get both a daytime and evening FP is to pull for first FP as soon as possible in the morning, so you get an early return time and can pull a second FP before they've run out.
Disclaimer: There have been some tweaks to the FP system recently since they've introduced MaxPass and I haven't been to the parks since then, so it's possible my info is out of date. I haven't seen anyone post about this rule changing though.