I am sure Fern and Bluerail were fine starting at 1600. But if your concern is temperature and not your work schedule, the low for the day is at sunrise. My default start time was 1-1/2 hours before sunrise. That gives you only a little over an hour of hiking in the dark, and about three hours of the lowest temperatures available. After that you rely on a lapse rate of about 3.7F/1000ft as you climb. Not that I ever hiked Skyline in July, August or September. I can well imagine that radiation from the rocks!
Here is the temperature history for the last three days at the Palm Springs Regional Airport:
https://www.weather.gov/wrh/timeseries?site=KPSP
Not sure what to say about water. I started carrying 5 quarts because it was recommended somewhere, perhaps on Perry's website. I found I never drank more than 4, with an average of about 3.5, and sometimes as low as 2.5-3 in the winter. But then I drank a bottle of Gatorade on the drive to the trailhead. I am of average size and a big sweater. Carried two Halo sweatbands and exchanged them frequently on warm days.