I've hunted them from daybreak through till dark and all hours in-between. They are active at night in the towns near here. Anytime is a good time; especially just after a rain. As far as a whistle, I would just wait for them to stand-up on their own, but give it a try. If it scares them away just quit using it LOL.

A small young groundhog here in VA would weigh about 4-7 lbs., but I guess the biggest I've killed would push 12-15 lbs. about the size of a good coon.