They'll be bedding in shady area's and north facing slopes. Under sagebrush/trees and cutbanks. Most hot weather muley hunting I've done required alot of walking and jumping them out of their beds. In my experience, they don't bed where they can be seen, so short to mid range shots are what you get. I've seen em jump from 400 yds away to as close as 3-5 yds away.
Not so much long range "range and dial" type of stuff, because when they get jumped out of a bed, they aren't usually hanging around very long. A running shot might be all you get, or they sometimes will stop just before going out of sight for one last look back. The distance they stop at might be 400 yds, it might be 800 yds.? If they haven't smelled you or directly seen you, they might stop at a closer distance.
Since you mentioned opening day, you might have some luck catching them moving up until mid morning, they get pushed around alot on opening day in my experience.
Good Luck, it's fun no matter how we do it.