I knew people whose toddlers stopped napping altogether at 24 months so at 20 months they might have been napping 2hrs but they might also have had shorter naps or a mix of naps and no-nap days. Certainly though it is young.
I wouldn't change anything in your routine and I would just put this down to it being the snowy days and his big brother being at home.
He may or may not take a catch up sleep when things go back to normal.