I have taken literally thousands of showers in America and that isn't consistent with my experience at all. If it takes more than ten seconds for my shower to heat up, it means that the water heater is dead and waiting any longer won't make a difference. The only place I've had to wait longer than that (but still not long enough that I'd go sit down to wait) is at some hotels, maybe because their plumbing is longer?
I grew up in a multi-story ~1700 sq ft home where I took daily showers on the second floor, traditional tanked hot water heater in the basement. Took < 20 seconds for water to turn hot.
