flower named 'Four o'clock'

I went shopping at a supermarket in the evening
--around 6:00p.m.

I saw oshiroi-bana along tamagawa-josui.
I know oshiroi-bana is called 'Four o'clock' in English.
Is it because that oshiroi-bana's buds open around 4:00p.m.?

(tamagawa-josui)