I did mine this morning (9am UK time so about 4am in Orlando) at my 60 day mark. It was very easy and intuitive. When I clicked on new FP+, it showed me my family and friends list and let me select the members from that group that I wanted to make selections for. It then let me select a park and date (although we could access the whole calendar, the dates of our resort stay were all highlighted and we could only select from those), then I selected the 3 attractions.
I selected the 'best fit' offered, then modified to suit my requirements. You can change time or experience very easily, though sometimes a bit of tinkering is required to move the slots around to fit exactly what you want. Apart from arrival day, I made all mine for mid morning to mid afternoon with the hope of picking up some 4th and even 5th passes at the kiosks - fingers and toes crossed!!
I got everything I wanted except a FP+ for 7 Dwarfs for the early evening of our arrival day - thought we might check into the Contemporary and head over there for our first ride, but no availability left although plenty for everything else (except Anna and Elsa and parade viewing) but got passes easily enough for 7D for days 5 and 8.
Happy planning!
