Thanks, @B_squared! I’ll let you know how it goes. Does this same rule apply to EMH at the other parks? I’m going to do a KTTK Tour the same day as EMH at MK…
Just now catching up with forum posts. I’d say the same applies for Hollywood Studios and Animal Kingdom, both are nearby. But for MK, I’d really want to be at the busstop 1 hour before RD. MK is a longer drive away, takes some time to walk up, get through bag check, etc., and then the awesome Welcome Show will begin around 15 minutes before RD. If you arrive a few minutes late, sure, the park will still be mostly empty, but early is awesome. 
Thank you for all of the insight! I am very excited for this trip!