The Grand Canyon is a spectacular sight!! The view has been diminished in recent years due to pollution, but it still is grand.
There are all sorts of levels of activities available. There are level walking paths that take you along the rim, more difficult ones that still keep you up top, and then it's possible to hike down into the canyon itself (one of my goals in life).
My sister and I got up early to watch the sun rise - definitely worth it, but make sure to wear warm clothes!! We were there in late May, but until the sun comes up, it's chilly!! The buses start running early enough so that you can catch a ride from the campground to a viewing spot. Afterwards, we hiked along the rim some, back towards the village area, and then stopped for some breakfast at one of the restaurants. It was very nice!!
We visited the south rim of the Grand Canyon for just one night; we got here in late afternoon and then left mid-morning the next day. It was our second visit, so I'd definitely recommend allowing more time for your first visit, but if you don't have more, stop by for the time you have anyway - it's definitely worth it!!
P.S. If you're going to be visiting more than two national parks (as we were), be sure to invest in a national parks’ pass - it's a good investment then!