It will take you about a hour or so to drive to the entrance gate of the South Rim and about a good 20-30 minutes to get to the Rim and (hopefully) find a parking spot. This time of year it will be crowded.
I would recommend, if you can, leave VERY early in the morning. You will miss the best of time of day there - sunrise - unless you drive up in the dark; and not sure when the gate opens. The shuttle to the west is great with all the stops.
We will be there once again this fall for 5 days; we love it there.
See
www.LaurensPix.com and click on Grand Canyon for a taste of what you will see.
Enjoy!