Took me about 20 minutes, but I have done it before, and I knew exactly what times I wanted for each attraction.
My procedure:
1 - Start with day that might have most difficult FP+ to get (Mine Train at MK)
2 - Pick the 3 attractions for entire group
3 - Of the 4 time options offered (A, B, C, D), pick the one that is farthest away from the time frame I want (we generally want FP+ in late morning/early afteroon, so I mostly picked the option with the late afternoon/evening times)
4 - Repeat Steps 1-3 for each of the remaining park days (I did Epcot days next, figuring that Test Track might be in high demand with Soarin closed)
5 - Then go back to the "most difficult" day (Mine Train) and Change the Time for the Mine Train to desired time, then change the times of the other two attractions to the desired time
6 - Then repeat Step 5 for each of the other days
I was able to switch every single attraction to exactly the hour-long window I had predetermined that I wanted, or a window that was only 5 or 10 minutes off from my plan (except two cases which were 15 minutes off from my original plan)
So now we're all set for the actual in-park experience when weather, ride breakdowns, illness, etc. waylay the best laid plans of mice and Mice-lovers....