I’m a little foggy on when I can book my 4th FP. Can I do it after I use my 3rd, even if I use the 3rd right at the beginning of my “1-hour window”? Or do I have to wait for the time to expire as well? So if my 3rd is at 11:00-12:00 noon time window, and I use it right at 11:00, can I then get my 4th at say 11:05?
You can start making the 4th one as soon as you scan in for your third. I was making FP+ for Splash in the line for BTMRR in early December so I know it works.
You can also modify your second to an earlier time once you tap in for your first and so on. On a day with extra FP+ availability, you could potentially finish all three in an hour IF you can find the earlier times for the rides you wanted.
But whether it's worth it depends what you are trying to pick up as your 4th FPP. If you keep checking there is a good chance you will pick up something someone else has cancelled, but it's a pain. I'd used my 3rd FPP by midday on a CL6 party day at MK, and all the major stuff down to Meeting Tinkerbel were gone, with only the likes of Dumbo available for near immeadiate start, which was perfect for us. There are always exceptions but I think that generally you will save more time by scheduling your FPP's later and making good use of the first 2 hours the park is open.
My experiences have been similar to @Tate. I never schedule FPPs for before 11:00. I use the first few hours to take full advantage of lower RD crowds and save my FPPs for the busier parts of the day. Between what I can do at RD and my FPPs, I've pretty much completed all of my "must-dos", so everything else is icing on the cake - including elusive 4th FPPs...
I intend to take full advantage of low crowds early. That goes without saying. Some of our FP will be for getting a second ride on our favorites. MK is the only park that I really have much interest in getting 4th or more FP. Unless I am extremely lucky, I don’t expect there to be anything good left at the tiered parks. I try to get the earlier FP because those are just plain hard to get. Then I have the option of trading for later times should I want to. Getting later ones and then trying to trade for earlier is darn near impossible.
Don't be so hard on the tiered parks. I was able to get a FPP for Soarin' at around 4pm one day for 6:30pm. Also got one for Fantasmic at about 3pm.
That's what I'm hoping for this February