Fantasy Land - First thing in the morning, especially if you have little ones.Attractions like Dumbo, Peter Pan and Winnie the Pooh get big lines fast! (Winnie the Pooh sometimes runs out of fastpasses.) Also, if you want to see the Little Mermaid for a photo, you should do this early - last week, there was a 1 hour wait around noon to see her.
The speedway should also be fairly early in the day.
You can get a fastpasses for Buzz Lightyear, which usually has a big line all day.
The other thing you asked about - not sure about the abbreviation. Big Thunder Mountain? This gets big lines by late morning but usually not as bad as Splash Mountain.
Basically you have to prioritize - what is the most important land/attraction for you to see, and then go there first. We were there President's week with very crowded conditions (many of the resorts were completely sold out), but between using fastpass and knowing which attractions to see early, we never waited more than 15 minutes for anything.
Have a wonderful vacation!
