We were only allowed to shower when she was in the bedroom (shower in en-suite) where she would wait in the bedroom and start counting the minutes down in her bedroom. Once 5 minutes was up she would shout to get out or barge in while I was in the shower.
This was done to "save money" at the time but looking back on it while we were on benefits we were definitely not poor (outlier case with high child maintenance and a paid off house due to accident) and there were no issues with money when she wanted a long hot bath every day.
I didn't think it was odd but the idea of doing this with own DC or a partner just seems absurd now I think about it. Even as a student where people were scraping by on £5-£10k a year absolutely no-one cared about how long people took in the shower (unless they needed to use ti obviously).