Hi!
I was there yesterday from open until around after midnight, with a break from 5pm to 8pm. Full disclosure, I was solo, and I don't really go on headliners, so not sure if that makes a difference.
FP+ was available all day. The first half of the day was REALLY smooth, until around 4 or 5pm when I left. I think that had a lot to do with the mine train being open all day as the demand was really high for that ride which made stand by's really manageable. Plus everyone in the world in line for Anna and Elsa all day.
I had FP's that started at around 11am, but I could have saved them for later and been fine. By the time my FP's started, I had already walked-on (or did really short waits) for all the rides I had FP for. So I just did two of them again when my FP times rolled around.
I saved one FP for later because I thought I would have some trouble getting one after I returned that evening, and I was right. I used my last FP+ on Jungle Cruise at 10PM, and then I wanted a 4th for HM around 11:30PM but it was unavailable until 1:45AM. There wasn't anything else on the list that I wanted. There were no mountains available either. I'm sorry, I can't specifically remember what was not available.
I ended up just declining the 4th FP+. Crowds were really high (by my standards -- I typically go to WDW in January so my idea of crowds is off) so I decided to leave around 12:30AM. I was not going to wait in a 30 minute line for a Dole Whip!
There was even a line for the PeopleMover which is one of my faves. I have never in all of my millions of visits seen a line for the PeopleMover!
Next year if they do this event again, I will plan my FP's for much later in the afternoon and try to do them all in one shot instead of spreading them out, so I have better chances for additional FP's.