1. Disney rides with Fastpass have 2 queues, Standby (normal) and Fastpass. Machines outside rides give out return time tickets. While the American parks will not let you in if you are really late (probably due to Fastpass+ coming in but also because people saved them for peak times. This is a pretty new rule.), DLP staff really do not seem to care despite the tickets having rather strict rules printed on them. I've used Thunder Mountain Fastpasses which expired 8 hours previously.
2. Day into timetable: yes this is one of the problems facing Fastpass+, more so because you can book ride slots months in advance. Breakdowns can also be a big problem with this system, hence the trialling on one ride. It's a pretty good choice of ride though since it's out of the way and forces guest movement across the park.