I have some experience with this system at the Grand Floridian back in January. We had arrived at the bus stop 45 minutes before EMH morning at AK. Monitor showed next AK bus arriving in 15 minutes. Looking good! As the time for the bus approached, the monitor updated the arrival time pushing it out 20 minutes. This kept happening for the next hour and 20 minutes until a bus for AK arrived AFTER all the magic from EMH had drained.
Hard to know if it is better to know a bus is not coming or hoping a bus is coming only to be disappointed when it doesn't.
BTW, is it just me or does Disney Transportation REDUCE capacity to parks with morning EMH? In my experience buses to parks WITHOUT morning EMH arrive with MUCH greater frequency than parks WITH morning EMH. Lately I have taken to calling Disney (number provided in MyDisneyExperience app) if I wait longer than 15 minutes for a bus. I am providing Disney with a realtime measure of demand. I like to think it helps. Better to light a candle than curse the dark.