Return windows for an individual cannot overlap, though different people in your party can have overlapping times (which answers the question as to whether or not everyone in your party must have the same FP+ attractions scheduled - no, they don't). But you, for example, cannot have a 4:30, 5:00 and 5:30. Your next scheduled FP cannot start earlier than your last return window ends. So you could have a 4:30-5:30, a 5:30-6:30 and a 6:30-7:30.
The latest return time I was able to schedule on a
MNSSHP night was 5:30-6:30, so would assume the same is true for
MVMCP. I imagine this is so they can clear the queue by 7. However, for things like A&E or 7DMT, the cutoff may be sooner; I can't speak to those from experience.
There are several
YouTube videos out there that will give you a look at the system and how to schedule prior to your FP night, but it really is very easy once you're in the system. Just make sure you go in with a plan of what you would like on what days - makes the process much faster. And if you are looking for A&E or 7DMT, start with your last MK day first for better chances and more available times.
Good luck - and feel free to ask as many questions as you need to get comfortable!!!