If the ground is going to be frozen in the AM there's no chance that I'm hunting a green field in the AM. I just try and focus on the pressure... Low pressure I'm hunting in the woods regardless of AM or PM. High pressure and the deer tend to want to feed more so a food source like a green field can be the ticket. As far as seeing mature bucks in green fields, I think if no shots have been fired in a field and there's been no pressure or disturbance to a field, it's a great place to see mature bucks, I've seen quite a few 4 yr old plus bucks killed in green fields when kept quiet... Unfortunately my club members don't care for this and just shoot does left and right in our food plots so we don't have much success as far as bucks go