Google up, u found plenty of articles about it instead of all personal opinion here.

But from my understanding, so far only our mother & grandma advice not to shower at night. No other sources stated that it's harmful to shower at night. Just make sure u don't open window and catch a cold after shower.

I'm abit skeptical too but I still shower no matter how late because I don't want any funny smell on my bed

Btw, how do u shower for 30 seconds? How fast can u apply shampoo all over ur hair or all over ur body? Faster than mandi kebau?