No offense, but this is a weird take. My wife and I both are in medical professions and work with patients with total joint replacements frequently. I have never heard anyone explain it like your friend. Does he have rheumatoid or another systemic arthritis issue that is affecting his other joints? I have spoken with patients who have returned to have the other knee/hip replaced after doing the first one previously and almost 100% of the time they tell me that if they had known how much better they felt after the surgery and rehab, they would have done it sooner. My father in law had one knee replaced around Halloween and then the second knee replaced just after New Year’s last year. By April, he was hiking in Sedona and went to Montana this past summer and hiked a lot with us with no issues with either knee. He had his shoulder replaced nearly 20 years ago and yes, the shoulder is a bigger deal. As far as the surgery, it is much more streamlined these days compared to several years ago. Rarely, do patients spend time in the hospital afterwards, unless they have other underlying health issues that require observation, then they spend the overnight at the most. Most total joint replacements these days are being performed in an outpatient surgery center. The patient gets spinal anesthesia, most times, with sedation. This is the anesthesia of choice unless, again, a underlying existing medical issue requires a different technique (Rarely). The patient will ambulate with a walker prior to discharge the same day as surgery. PT wil begin later the same day or first thing the following day. The quicker the patient is moving the joint, the better the outcome. As far as how long for recovery, as the original OP asked, that’s beyond my experience, so I’m sorry but I can’t speak to that. Hope this helped. Just my experience. Good luck to those who are considering the procedure.
FYI. Do your PT after religiously. Do it as long as you can. Do not cut it short even if you think it is unnecessary. Your outcome will be far better if you see it through.