I prefer to hunt in the morning as well. I like to get in the woods when it is still dark so that the squirrels will never know that I am there.
At the first light of morning the squirrels that are leaving the den trees and nests are usually moving pretty good trying to get to thier destination. However, in the late evening as the squirrels return to their dens they will usually move slower and sit around more near the tree.
Other than this there isn't much difference between evening and morning.