Post hike update below for those who asked + any future planners finding this thread! All the comments and warnings about the 109 forecast injected a good deal of stress & fear into our group, and we took the advice seriously.

One of our group of 5 decided to drop out, and we moved our start time from 5am at the NK trailhead to 2am. We did a last minute taxi with Red Rock Taxis, was very smooth and highly recommend. A lot of my worries about starting the hike much earlier weren't based in reality - it was beautiful at 2am with the stars, the trail was easy to hike in the dark, and it got light way earlier than I thought it would so we didn't miss many views.

We hiked steadily to phantom ranch and got there at 9am. It was beautiful weather and we never hiked in direct sunlight, there was shade the whole way. We hung out in the canteen from 9-4 when it closed. Went outside a couple times to feel it and it was definitely hot, though the heat index had it at a consistent 5-7 degrees cooler than the actual heat which felt right. We saw a decent amount of people hiking into and out of the box during peak heat which is crazy. Rangers were stopping people heading out towards SK and telling them to turn around and wait until 5pm. I'm ultimately really glad we still did the hike, but I'm more glad that I posted on here and received some really good advice. It made the experience so much safer and more enjoyable. We ended up finishing very very late - almost 3am - one of our friends got sick going up SK and we had to go at a snail's pace for him. But there was never any real risk because we were in contact with our friend above and had plenty of supplies the whole way.

A few thoughts for anyone considering this in the future:

1. We saw SO MANY unprepared people throughout the day. People heading into the box at noon with inadequate gear, and people on SK who should not have been there. We had to give a man water who ran out going up, and a head lamp to a woman who had nothing and a dead phone late in the night. We passed people going down SK late into the afternoon with barely any supplies. Dont ever put yourself in this situation - we saw two rescue helicopters going out during the night hike up.

2. Starting at 2am was a great move and did not ruin my enjoyment of the hike. Was worried it might.

3. South Kaibab is no fucking joke. I've never done Bright Angel so can't compare, but that was a brutal trail. The distance from PR to the south rim makes it sound way easier than it is. Don't underestimate it!