And for those who have the time and patience to try to get exactly what you want, here are my tips for doing it:
What I finally discovered was the best thing to do was:
!) Select the initial group which was FURTHEST AWAY in time from the time frame that I really wanted, regardless of what attractions were listed in that group.
2) THEN change each individual attraction to the attraction I wanted and THEN change it to the time I wanted (there would then be lots of hour-windows to choose from, because there was no conflict between those times and the times in the initial group).
Does that make sense?
In other words, if the initial group had, for example, Tower of Terror from 10:50 to 11:50, and I wanted to change Toy Story Mania to an 10:00-11:00 time frame, that time would not be available because it overlapped with my initial Tower of Terror time frame. So then if I decided I better change the Tower of Terror FIRST, I might still have a problem getting a time I wanted for it because it conflicted with the third attraction in the initial group.
So just best to start out picking an initial time frame I DIDN'T want at all (even with attractions that I didn't want), and then I had maximum flexibility in getting the attractions I wanted at the times I wanted.