Personal preference and the park you are going to be in that day. We like to do ours in MK early. MK has enough FP+ attractions, that you can pick up some useful ones for a 4th or even a 5th or 6th. That park we have done really well by getting them early and going for more. The rest of the parks, I don't know that it makes that much difference. We do not go at really busy times, and we have never had luck with a 4th at either EPCOT or DHS. EPCOT, I have loaded them first thing in the morning many times trying to get a 4th FP+ for a Tier 1 attraction, and I have never once been successful in doing so. It drives us nuts not to be able to FP+ Soarin and TT in the same day. I don't know what we would do if DD was too young for the single rider line. I will say though that there was one afternoon that was not even a busy day that the line for Figment was 30 minutes. That time it was useful because I grabbed a 4th FP+ for Figment that kicked in 30 minutes later for Figment and then we shopped at Mouse Gears until it was time to ride. That was better than standing in line. I never thought we would find ourselves needing a FP+ for Figment as before FP+ we had been walking on it for years. At DHS, I have loaded them early in hopes of getting a FP+ for Tier 1 RNRC (we always use our Tier 1 for TSM for DD), and I have never been able to get ANY 4th FP+ for DHS at all, and certainly not the one I wanted. I get the lovely no availability message at the kiosk. AK, there are not more than 3 things we want to FP+ anyway. That park we might start them a little later as we can go get a ride on Safari at rope drop with a short line and then do it again later with a FP+.