Most people think I'm backpacking I can leave anytime but if you leave late in the heat of the day there is a price to pay. You can mitigate the heat of a late start by taking strategic breaks, at Lone Pine Creek at the top of the lower switchback, along Lone Pine Creek in Outpost Camp and at Trailside Meadow. I makes for a longer but more enjoyable trip.
BTW, what happens when the DEET, sunscreen or water filter person beats feet back to WP with the mother of all cases of AMS? We used to do the you do this, I'll do that thingy and found out if someone has to turn around or extraordinary circumstances arrive it's a good thing having a partner with...moleskin, toilet paper, DEET, sunscreen or a Steripen with good batteries to save the day.