You have got me curious I will need to explain "why" to our group. Why is this? ...and thank you!
OP Here is the thing.
Fantasyland has rides that are extremely popular with long waits: Peter Pan's Flight, Seven Dwarfs Mine Train, and Many Adventures of Winnie the Pooh. Then there are rides like Enchanted Tales with Belle, Under the Sea--Journey of the Little Mermaid, and Barnstormer, which are rides you definitely want to hit as early as possible before lines build up. Dumbo and It's a Small World can sometimes have lines up to 25-30 min on really peak days, but usually ride those after lunch or in the afternoon.
Tomorrowland also has a lot of rides that are popular. Space Mountain obviously is a really popular ride, and lines average around 60 min in the middle of the day. Then Buzz Lightyear's Space Ranger Spin and Tomorrowland Speedway are not just rides you can wait standby anytime in the day. Lines average around 30 min for those. Astro Orbiter and Monsters Inc can have lines with an average of 20 min waits. Carrousel of Progress, Stich's Great Escape, and Tomorrowland Transit Authority are easy to do anytime but the duration of those attractions is longer.
Frontierland has two huge headliners: Big Thunder Mountain and Splash Mountain. Both of those are great rides and you will likely want to do them twice. But even if once is enough, you will have to either hit BTMR at rope drop or Fastpass it. Splash Mountain is always best to do with a Fastpass in the afternoon because you can get wet on that ride, and the middle of the day is best. Again lines for BTMR average around 45-50 min, and for Splash Mountain between 55-65 min. Then you have Tom Sawyer Island which is definitely not to be rushed. There are a number of cool things and you should take your time on that and plan to spend at least 45 min exploring it.
Liberty Square has three rides: Riverboat, Hall of Presidents, and Haunted Mansion. To tell you the truth the Haunted Mansion is the only ride I care for. Riverboat is really just an extremely crowded big boat that just sails around, and its not worth doing. Hall of Presidents is not that interesting either. Haunted Mansion has average wait between 30-35 min. Good one to use a Fastpass for.
Adventureland is usually the quietest out of all areas, and you can pretty much do everything there anytime in the day. Pirates of the Caribbean lines RARELY exceed 25 min, and the average is about 15-20 min wait. Sometimes its as low as 10 min even, and I actually just walked on during the 3pm parade back in the summer. Jungle Cruise can have lines like 20-25 min, but its quite easy to do anytime, and that is almost always a ride you can get an additional FP+ for if you need to. Then there is the Magic Carpets of Aladdin, Enchanted Tiki Room, and Swiss Family Treehouse which hardly have a wait.
So if you use your head and think about it, you will understand why Fantasyland and Tomorrowland cannot be done on the same day especially in the little time your trying to cram them. As I said before Fantasyland should be done one day, and the Mountains on the other day. Adventureland is good to pair with Fantasyland because when your done, you can relax and not worry about long waits in Adventureland. Then usually the second day I would rope drop BTMR and have an early FP+ for Splash after lunch, and do Country Bear Jamboree, and Tom Sawyer Island in the morning. Tom Sawyer Island is the quietest and best in the late morning. Then go to tomorrowland in the afternoon using FP+ for Space Mountain and Buzz Lightyear while hopping on the other rides working around.
