I'd have to see the data to prove those observations, but if it were true, there is no reason I can think of why it would be true.
I think one thing that might help to give this observation is that when a storm happens during the day, you are looking at the snow gradually build up, whereas when a storm happens overnight, you wake up to all that new snow that seemed to appear instantly.
I know the big storm that hit Chicago in 1999, most of it happened during the day.
-John