I can speak for the USN.
There used to be a TV ad for the US Navy that said, "we do more before 10 a.m. than most people do all day." It's pretty much true.
I would echo the post above. Also, most military schedules are "front loaded" in that days tend to start before 0800. If you drive by the Pentagon at 0600 there are lots of cars already there; by 0800, the parking lot is full. By 1600 (4 pm), it's starting to empty considerably. By 1800 (6 pm), basically only the watchstanders are still around. The same tends to be true on ships and in squadrons.
One thing the military "teaches" you is to become a "morning person." Even if you aren't now, you will be. As a civilian, I still arrive at work before 8 even though our normal working hours don't start until 9.