I did a rim to rim...went down the South Kaibab trail to Phantom Ranch, and then back out on Bright Angel...in the same day. It was June tho...not quite 120 degrees at the time. Although the bottom of the canyon was in the low 100’s. It would have been nice to cool down in the river, but the water temp was in the low 50’s.
It was epic...but I was a mite younger in those days.
Funny thing...there are signs posted several places all the way down the trail, warning people to not attempt to hike down and back out in the same day. People that get stuck doing that have only two options to get back out...mule train from the ranch or helicopter. Not a cheap trek.
“It’s the second potentially heat-related death this year in the Grand Canyon.”
You were fortunate to do that hike before Global Warming was a thing.