Why does the SV* always hit late at night??

[k10]

I feel like it doesn't have anything to do with the incubation period. The incubation period for noro is 12 - 72 hours, so it could start showing symptoms at literally any hour after 12. It's not like it waits until the 24th, 36th, or 48th hour and decides it's time to make you v* now. You know? It could be any time. But its almost always night!