At The Woodlands HS, just north of Houston, practice always started at 6:15am. We typically started running by 6:30 to 6:45am. We did all of our hard workouts, long runs, tempo runs, everything hard in the morning, almost year-round. We did doubles almost every single day during the school year but these were only 3 - 5 mile recovery runs. We started at 4 to 4:30 PM and on the hottest of days even a very slow 4 mile recovery run could be absolutely miserable. I specifically remember one afternoon my sophomore year when it was 111 outside (without heat index) and we still did our afternoon recovery run outside. It was tough but we dealt with it ok and it made us think we were tougher than other people.
We were once on a long hard run (13 miler) and it was an exceptionally humid morning. Coach (on the bike) started theorizing that running in such humid conditions was similar to running at altitude. He didn't speculate that you got the same benefits as training at altitude, but that the increased effort to run in those conditions was similar to the extra effort required at altitude. This was perhaps just another way to make us believe we were training harder than anyone in the country, and while it may hold no water at all, we believed it, and thought we were tougher for it.
I do recall one day, one day in 4 years, that it was SO hot the athletic director called off ALL practices outdoors for the day. We ran 4 miles through the hallways......good thing our school was big.