Installing composition shingles in very warm or hot weather requires special considerations. All composition shingles become soft in the heat and scuff or scar very easily with foot traffic. This severely compromises the integrity of the shingles and will shorten their lifespan.
DO NOT allow anyone on your composition roof in hot weather unless absolutely necessary. Tell them to wear soft shoes with smooth soles and not to twist their feet back and forth. Walk CAREFULLY.
In extremely hot climates like Southern Arizona, roofers will be on the roof by dawn, quit at mid-to-late morning, then return later in the day, even working under lights after sunset.
A way to beat the heat in the Pacific Northwest is to stay on the shady sections and relocate when the direct sun comes your way. Some roofers will keep a hose nearby and hose off the shingles periodically, which will stiffen the shingles and lessen the chance of scarring.
I used to save the plywood offcuts from previous roofing jobs. Then I made plywood trails on the roof and kept as much foot traffic on the trails as possible. Little tricks of the trade!