The
resort monorail line
will run throughout the day.
The
express monorail line (that goes from TTC to MK and back with no other stops in between) is the one with the
modified schedule. On rare occasions, the resort monorail line might break down for awhile...but no way to predict that.
Keep in mind when planning MK monorail resorts, how many stops the resort monorail line will make (5)...
MK--to--CR--to--TTC--to--Poly--to--GF--to--MK...and around all over again...
And as previously mentioned, when going to EPCOT, you have to get off at TTC...walk down the ramp, around, and back up the other ramp to wait for the EPCOT monorail. You might get lucky and be able to take the easy pass-through from one monorail line to the other...but I haven't had that luck in several years worth of trips. We typically have to walk down and around and back up on the other side.
We like the monorail and enjoy having it as an option when staying at MK resorts. We have just learned when it's best to use it and when it's best to boat or walk (or buses if they're an option).
For example, we rarely use the monorail to get to or from MK and CR. We can certainly walk to MK from CR faster than it takes us to make the entire resort monorail loop. And there are just so many times that I can hear, "Please stand clear of the doors. Por favor, mantengase alejado de las puertas..." before I'm chanting it over and over in my head all day (and all night in my dreams)...

We also typically just walk back to CR from MK. It's a pretty good little jaunt just to get over to the monorail platforms from the MK exits. By the time you walk to the exit and then over to the monorail ramps, and then UP the monorail ramps, and then stand in line to catch the monorail...we'd be back AT the resort.
Another example: When staying at GF, we like to take the monorail to MK since it's the first stop...but prefer taking the boat back to GF from MK

(unfortunately, walking isn't an option between those two places...yet...or probably ever).
This might be a fun option....
...or maybe

(I hear that Uber prices are pretty cheap

)