Not in the military, but when I need a quick shower, two minutes tops is all I need. Get wet, soap up, rinse off. (It probably helps that I lived for several months where there was no hot water for showering, so you wanted to spend as little time as possible under the shower, unless you were a masochist.) Typically, though, I like my long, hot showers, or, preferably, a bath. If you’re including a shave in that, well, that’s going to take about 3 minutes itself.
Not in the military but on a training ship for the US merchant marine. We had restricted showers. We had the evaporators making water almost all the time. The temperature discharged from the evaps was 120 degrees. The water went into the domestic water tank. Which had a boiler room on one side 130+ degrees. Auxiliary spaces two sides. One side with the boiler water tank (evap water). And double bottom tanks with boiler make up water under the tank. so the cold water on the ship was not really cold.
I learned to take a combined fresh and salt water shower. After a watch in the hot engine-boiler room I would wet down with fresh water cold only. turn water off soap up then rinse off with fresh water. Then step into the salt water shower to cool down and stay there as long as I wanted. Then step back into a fresh water shower to rinse the salt water off.
On a ship fresh water is a expensive thing. If the watch goofed and the evaps flashed over. That is the discharge is not pure, that water then became domestic water. Have you ever had salty coffee?
If there is potential time difference, I’d think it isn’t so much the length of hair, but the thickness of it – “Thickness” meaning how densely-packed your hair is on your scalp, not the texture of the strands of hair itself.
Like you, I never wash my hair daily. When I take a shower-cap shower, I can be done in just a couple/few minutes, but hair-wash showers are guaranteed to be a minimum of 10 minutes. I have ridiculously thick hair that is long, straight and fine. When it gets wet, it all sticks together in one thick, heavy mass because it doesn’t have any wave or curl to separate a bit like this cheesy stock photo woman’s hair. 
It takes a lot of time to actually work the shampoo through/over my entire scalp and again to completely rinse it out (and then again with conditioner for the length of my hair).
When I was in boot camp, yeah, it took about that long. I hit everything - you just get wet, apply a bit of soap to all skin (takes about 60 seconds - don’t forget your ass crack), then rinse off. Your hair just needs a tiny bit of shampoo or you can just use bar soap on your hair when you have so little of it.
Air Force in 1981 … I seem to remember there wasn’t so much a limit to individual times, rather the showers had to be pristine clean at lights-out.
Ships at sea need to make sure they have enough fresh water for the boilers, only if any is left over are the seamen allowed to shower, that was my dad’s WWII story.
Your shower in the morning after PT is nit a luxurious time for loofah and conditioner. Rinse hair, wash body, out. Any longer, and you are taking time from someone else. If you want time to shave/deep condition or mask, you do that later during personal time.
Governor Brown (California) recommends short showers: Governor of California
“Boot Camp showers… It’s not just for the military, anymore!”
Once a week? What, do you work at the dump and swim in the sewer? I do once a month and my hair stylist loves my hair.
Brown can go fuck himself.
I could rival Saudi Arabia with the oil in my hair after just 24 hours.
I don’t know about these days, but the showers we had in bootcamp and onboard ship were somewhat self-limiting.
Here’s an image of one
(and I couldn’t find a single image of one close up. Nobody ever posted a photo of a Navy shower head?)
The problem was that there was a push button on the side of the handheld shower head that you would hold with your thumb for as long as you wanted water. It emitted a weak spray, and your thumb got tired, so it was good for the “get wet, soap up, get wet again, dry off” approach.
As it turned out, some of the fellows found out that if you pried open one of those cheap pear-shaped shower curtain rings, you could stretch it around the shower head, forming a spring that would hold the button in. Then you could wedge the shower head in the pipes and … Bob’s your uncle.
Depends on your hair type. My hair is baby-fine and gets too greasy if I don’t wash it every day. Sorry, no. I’m not willing to go a few weeks to test out that theory.
Despite my not washing my hair daily I do take time enough in the shower to make sure I am fresh everywhere so I don’t end up with armpit vagina stank.
My showers nowadays usually take about eight minutes, but I can take shorter ones when I have to (and often did at Scout camp, back in the day, because the water was always $*%&^#! freezing).