I've done 2 in a day twice now. I always plan them, I call them doubleheaders. I choose providers who are opposite ends of the spectrum in body size, race, newbie vs experienced, role play etc.
Three a couple of times. One day I had four planned, but the third insisted I stick around, so by the time I got over to the fourth I knew it may not work. The last girl I visited I had seen a few times before and I knew she had excellent skills, but even she could not get him going. She was very upset about it as she prided herself on her skills. I was probably early 50's when I tried this, so now that I'm five years older I will not try again.