Hi, if you stay at the Phantom Ranch overnight and aren't carrying pack, the Grand Canyon is easy to do in two days. If you take the Kaibab Trail, it's ~7 miles each way. (However, if you can't call a 7 mile hike easy under any circumstances, don't attempt this).
Here's how you do it. Start at the top about 5:00 or 6:00 am with a headlamp, and you'll be at the bottom by noon and avoid most of the heat (gets hotter the lower you get).
Have a protein breakfast, NOT pancakes. Drink at least a liter before you start the trail, better to drink two. Carry four more liters in a hydration pack, and be sure to add a powdered supplement to replish electrolytes.
Also carry two snickers bars each, plus whatever you're having for lunch. Wear a hat, sunscreen, and sunglasses. And carry a change of undewear and a clean shirt for the next day. At Phantom Ranch, you can buy ALL other ammenities you might need. The showers have soaps and towels, the cabins have all the bedding you could use.
Phantom Ranch bunkhouses are not co-ed, but have greater vacancy. The cabins are bunk beds and wonderful, but much harder to get.