Hello!
I ran/hiked North Kaibab to Bright Angel last weekend. I started early (4:30), and didn’t feel the need to stop until I reached the Cottonwood water stop. I think that was about 6 miles into the run? I think you should take a break when you feel you need it. After my short break to fill water and eat a snack, I ran to Phantom Ranch (7 miles) without a break. I obviously stopped to take a few pictures… My goal was to keep a pace that I could maintain all day. I took a few more breaks on my way out of the canyon, since it was really hot.
My advice is:
-Break when you feel your body needs the break.
-Make sure you have enough water to get to Phantom. There is a water stop at Phantom Ranch, and there are 3 water stops on the way up Bright Angel.
-Start early to avoid the heat.
I live in Flagstaff! Let me know if you need anything.