The transportation was so hard to predict. I think Disney suggests 90 minutes just so you have enough cushion, especially if you need to take multiple modes of transportation, pass security checkpoints, and actually get to your destination.
I was very fortunate that I did not have to wait more than 5 minutes for any of my busses from the Poly to HS, AK, or even Epcot one morning the Epcot beam was closed for maintenance. We just happened to walk out of the great ceremonial house at the right time. My worst transportation experience was waiting at HS to go back to Poly. Had to have been at least 25 minutes of waiting, and there was a family there before us who had waited at least 10 minutes prior at the GF/Poly stop. The bus finally came, and another one cut it them off, so it then had to go all the way around again until it could park. Additionally, if you have anyone with a stroller or
ECV, this will add time to unload, load, and then unload again.
The monorail seemed to be fine for me, except on a day the express was down for maintenance. The resort line became packed and I had to wait for the next one. Not a big deal, but added a little bit of time.
The boats were probably the least convenient from my experience. Probably because 2 out of the 3 times we took them was because something was closed so extra people were cramming in. The boats also take much longer. If you want an experience and are willing to take more time out, go for the boat! If you want to get somewhere as fast as possible, avoid the boat (IMO).
I am planning on utilizing an Uber for Disney Springs, or to get from resort to resort. You can get some decent Uber credits if you a are a new member, refer a friend or family member, or sign up with a Chase credit card! I know I am the only person in my travel group that currently has an account so I can refer them all and we can probably go our entire trip for free. One side note, I think I read Uber could not pickup at MCO. Not sure if I remember that correctly or if it also includes dropping off. I would check the transportation thread!
Yes, we found the monorail ride to be very convenient to the GF from the Poly. And that lobby is very impressive when you walk in on the second floor! It is the reason our December trip is booked there! The whole time we were walking to our meal my mom kept saying how she could see herself staying there. I can only imagine what it would look like with the tree up in person! The 5:35 may be a better option to plan for the unknown. You could even get there very early and try to check-in for the 5:35 rather than be on time for the 5:15.