500 am to 5pm? I guess its possible, if there is no traffic and no delays esp going thru Flagstaff, but you wont spend much time actually at the rim after parking, after stopping for lunch and potty breaks, and you certainly wont have any time to be able to go down the canyon at all.
By the time you pay for the car, the gas, the hotel(if it takes longer than you expect?), etc, (not to mention losing 2 days and a nite away from Las Vegas?) you would be paying almost as much as it costs to take a helicopter ride to the Grand Canyon. There is really not much to see on the way by driving, except a lot of desert, and the same desert on the way back.
The telescope in Flagstaff is interesting to see, the telescope that discovered Pluto. When I was there, it still revolved by using old car tires.
The helicopter ride is fun, quick, there is more to see from the air, Hoover Dam, Lake Powell(?), boats, deserts and forests around Flagstaff, wild animals as you fly over them, the indians where you land give a lunch at the bottom of the canyon, and your back in Vegas by early afternoon.
The Canyon is a big hole all right(7 miles wide and 200 miles long seems much too big to be made from that little tiny Colorado river at the bottom, if you can see it) , but I found Meteor Crater, just a little farther to the east in Winslow(?), much more interesting.
It takes half a day just to drive to Hoover Dam right outside of Vegas, and see that.
Driving to the South Rim of the Grand Canyon and back in 12 hours is pushing it. You will spend all morning driving to it, get out and look at it for a few minutes, and then spend the rest of the day driving all the way back.
I recommend driving to Hoover Dam on one morning, and then taking a helicopter ride to the Grand Canyon on another morning.