Planning to do it in mid-June. The timing isn’t optimal, but it’s the only opportunity I’ll have in the foreseeable future.
* Day 1 — shuttle to North Rim, stay in campground, food at nearby store, use old gear that can be thrown away/given away afterward
* Day 2 — start down the North Kaibab Trail at 3 a.m. ETA at Roaring Springs (4.7 miles in): 5 a.m. (took less than two hours the last time i did this part of the hike)
As soon as it’s light enough to see, run to Phantom Ranch (9.5 miles) Estimated arrival time: 7 a.m. (never done this section)
Hike up Bright Angel Trail to the South Rim and my vehicle (9.6 miles) ETA: noon (took less than five hours the last time I did this part of the trip
Additional info: I’m used to the heat. It was 105 degrees here in the Southwest yesterday when I left work. I do a lot of trail running (often with 3,000-4,000 feet of elevation gain, and once it was 8,000 feet). I do a descent amount of mountaineering. Very familiar with hydration, nutrition, foot care, heat issues. Have done SK—PR—BA before, as well as NR—Roaring Springs—NR, so I’m familiar with much of the terrain.
That's 9 hours so it is very doable. We did south to north in 11 1/2 hours which was just pretty straight forward hiking without much stopping. As a solo hike pushing it a little this should not be much of a problem for someone with experience.
Good rule of thumb: Phantom Ranch's daytime high temperature is about the same as in Phoenix.
Being used to 100+ F heat is one thing, hiking up many thousands of feet of elevation in it is another. Be extremely careful. If it happens to be particularly hot, e.g. 110 F or higher, consider laying low at the bottom and then ascending at dawn the next day.
My 1st R2R was in 2001. Drove to the N rim, stayed in a cheap cabin, started early, got to Phantom Ranch when it was over 114F. We went up S Kaibab (mistake -- meant to go up Bright Angel), hid in shade every opportunity we had. Got to the S rim, took a free shuttle to cheap motel at town to S in Tusayan. Next day took a free shuttle to pick up the trans-canyon shuttle back to our car on N rim.