When I was in high school, my older sister returned home after completing nurse's training. She was the queen of long hot showers and would use up the entire tank. My complaints fell on deaf ears.
I began going into the basement and slowly turning off the hot water supply. It was great fun hearing her complaints begin as the shower cooled. After a week or so, her shower time automatically shortened. I again got a hot shower when I got up.
No particular point, just a fond memory of sibling conflict.
How to Stop Taking Long Hot Showers?
Re: How to Stop Taking Long Hot Showers?
^^ Per the OP and your observation of your sister's shower habits, I think there is a psychological component to it. We wash the day off before we get in bed and sleep it off.
Re: How to Stop Taking Long Hot Showers?
Turn off the water heater. Or turn it way down.