Clausewitz, On War, Book 2: A Question

I know this is a bit late, and if I missed the answer in someone else’s post, I’m sorry for bringing it up again. It’s a minor point perhaps, but on page 143 Clausewitz states that both time of day and weather are of minor importance in the engagement. This runs counter to what intuition would suggest. Can someone explain to me why Clausewitz says this is so?