We spent 3 days there. The first day we drove there and got to the canyon in early afternoon. We wandered around the main Grand Canyon Village area but didn't get on any of the transit buses for trips to other areas. We returned to our hotel that night (Best Western in the village, about 5 miles south of the canyon) and had a great dinner there.
The second day I got up around 4:30 and was in the park along the canyon rim well before the sun came up so I could photograph the rising sun and changing scenery in the canyon itself. It was worth getting up!
We spent the second day touring the GC Village and riding the tour buses along Hermit Road to the west end of that part of the park. We had dinner that night at El Tovar which sits right at the edge of the canyon. Spectacular food and great views as the sun was setting.
The third day we took off and drove out to the eastern viewpoints then back to our condo in the Phoenix area.
We didn't do any hiking because these old knees aren't up to it. If you're doing any hiking, five days would be about right. If you're not hiking you can pretty much see the canyon in three.
Here are a couple of videos I took on the second morning.