JDM from ND on 3/20/2023 9:29:25 AM:
It is entirely possible to ride it in one day for very well prepared people. I was in descent shape when we did the trail, but we still split it up into 4 (3?) days. Memory a little fuzzy, but I know we powered thru the last day and finished a day earlier than planned.
Granted, we were 4 adults and 4 kids, so there were other limitations, but most days, I was ready to be done with it.
Being your first time, my recommendation is to ride the opposite way (Deadwood to Edgemont) as it predominantly downhill:
https://bikemickelson.com/elevation.aspx