Sometimes I hear women say "Oh, I can't go out tonight, I have to wash my hair". What's so complicated about this washing of hair?

Ok, yes, this is mostly on tv. But, it still begs the question: Why is this such a hard task that it requires someone to set aside a night a week or two just for doing it? Is washing your hair not a 3 minute part of every woman’s daily shower, but rather some hours-long project to be undertaken, like cleaning the house? Is it only when women wear wigs, and the wigs need special care, and this is some discrete way of letting everyone know that their hair is fake? Is it code for something else, like dying the hair? Is it code for something “unsavory”, like since women aren’t ever supposed to poo, it secretly means “I haven’t pooped in a week, so that’s gonna take me a few hours to be done with” or “I’m going to be having really uncomfortable, somewhat freaky, totally obligatory sex with my husband”? What is the deal with this taking an entire night off to “wash one’s hair”?