I think your uncle will find his day will run very smooth and most likely very non eventful. He will be made quite comfortable during the process.
I've read many posts and know of a few people who were in and out within a few hours. A friend I met through our local support group, arrived at 5:30 a.m., had his treatment and was out in time to walk to a restaurant and meet a friend for lunch!!
In my case I arrived at 5:30 a.m., had the head frame attached pretty much immediately, but did not have my treatment until 2 p.m. Having to sit around for so long to have my treatment, made it a rather boring day. You can't wear your glasses when the frame is on, so taking a book to read is a waste of time. Taking an Ipod to listen to music would be handy or just having someone with you to chat with helps pass the time. I unfortunately had a nasty headache immediately following the treatment when the head frame came off - they do warn you this can sometimes happen. I was given something for pain and nausea through IV, an ice pack on the back of my neck and I slept for an hour. I woke up and felt fine, no pain. My sister and a girlfriend were with me and drove me home. I had something to eat when I got home and went to bed to sleep. The next day I felt just fine. The following day I woke to swollen eyes that required ice packs to bring the swelling down. I had no other issues. Pin sites healed beautifully, no complications!
I'm sure your uncle will be fine. It really is much easier than we expect it to be.
Best of luck.
Cathie