Let's, once more, put this heat thing in perspective. Here's the average weather for Leon on Aug 3, historically the hottest day of the year.
"August 3 Weather in León Spain
On August 3, the temperature in León typically ranges from 55°F to 80°F and is rarely below 49°F or above 88°F.
For reference, on August 3, the hottest day of the year, temperatures in León typically range from 55°F to 80°F, while on January 20, the coldest day of the year, they range from 32°F to 45°F.
The coolest time of the day is from 3:00 AM to 9:15 AM, with the coldest at 7:15 AM, at which time the temperature is below 58°F three days out of four, and below 61°F nine days out of ten.
The warmest time of the day is from 1:30 PM to 8:30 PM, with the hottest at 5:15 PM, at which time the temperature is above 75°F three days out of four, and above 70°F nine days out of ten.
The day has gained half its heat by 11:00 AM and lost it again by 10:30 PM."
And here's a 24 hour graph showing average temps for August 3.
At noon the average temp is 70 rising to 78 by 3:00. Most people replying to this thread report starting about 6:00 am. So, at the end of six hours of walking the average temp is 70. And 78 after nine hours walking. I saw this pattern repeatedly during last summer's week-long heat wave. The hottest time of the day is typically about 4:30-5:30--here is this historical record, the hottest time of the day was 5:15.
And here's 12-month average temps, from March when the average high is 43.6 to July/August when the average highs are 68.3.
But, but the heat wave! Even during a heat wave (which we experienced in July last year--I wrote about it from Hontanas in a July, 2022 post), the morning to afternoon slope is pretty much the same, except for maximum temperatures at the 4:30-5:30 pm bewitching hour. Even during the heatwave last year when many people were leaving by 6:00, the temps had barely reached 80 by 1:00.
Assuming one can be comfortable in the average temp ranges in August 56.6 low to 68.3 high . . . well, more than an assumption I have to think everyone is comfortable at 68.3.
So, even with the occasional heat wave, it's simply a matter of avoiding walking mid to late afternoon. If you're leaving at 4:00 to 6:00 in the morning, that's 6-8 hours walking by noon which means you'll be sitting under an umbrella sipping a cold beer or sangria well before the hottest part of the day.
And here's the best part for the "Camino is too crowded crowd"--except after Sarria (and those damn Spanish school kids enjoying themselves and disturbing us), last year July was decidedly not crowded. Beds/rooms aplenty. Some days I barely saw 25 other pilgrims.