Edward,
Welcome to HW
I had a DaVinci RP, and can just relate my experience.
The surgery, anesthesia, and pain meds all impact the intestines and rectum. I was told to expect some constipation, and pain in the rectum. Because of past colon issues, I was already taking a daily stool softener (docusate calcium), and the surgeon was agreeable to continuing that one, even while I was in the hospital (4 days - longer than most).
My first bm was before I left the hospital. I found the bigger issue to be dealing with bladder spasms and leakage around the catheter during the bm, but that was manageable.
Some members have suggested getting a raised/split home care style seat for the toilet, but I did not find that to be seriously needed (might have been nice).
Avoiding a hard stool is essential, as the prostate is against the rectum, and removing it leaves a part with little support, thus fragile. You do not want to develop a fissure/fistula. Better to go often than have problems.