Hit the trail around 5AM. Headlamp is helpful for the first stretch. It'll be chilly at the start but over the first hour I shed my light rain jacket and long sleeve t and from then on it's shorts and a t-shirt. I wear trail runners and that seems to be the most common footwear. I don't like camelbaks so I just carry a large water bottle plus a couple gatorade bottles. Plenty of water stops along the way but check current status just before you go since some stations get shut down from time to time. Haven't found an electrolyte powder I like so I just do gatorade powder, plus trail mix, pbj, fruit, some jerky or something. Rest a little at Phantom Ranch and finish by late afternoon.

About a month before rim to rim I like to hike Timp, which is a good indicator of fitness and readiness (not accessible this time of year but I'd look for something comparable). If you can do Timp and not be completely knocked out you should be good for R2R. For shorter training hikes Y Mountain is really good. The steep climb is pretty similar to what you face at the end of the Grand Canyon. If you're used to hiking poles you'll appreciate them on this hike, but it's probably not the best time to try them out. (I don't use them.)

I assume you've prepared and are sufficiently fit. If not, you'll want to reschedule.