I would love to know why this is titled "It's American Time". It really confuses the hell outta me.
I would presume because Americans (as well as pretty much everyone outside of Japan, but I guess most foreigners are American to them...) wash their hair while in the shower/bath, rather than having a separate area to do all the cleaning before you get in the bath to superfluously soak.
Naturally, the nature of this series is to turn everything up to 11, so they dive head-first into a bathtub...