If you are quite and not in sight of them you can set up most anytime, but the early morning hours are the most sensitive cause they are on roost and scanning for threats, to see where they will fly down. I set up late morning on some birds I had seen in a field, and simply waited until they moved down the tree line around a point and out of sight. An hour later they came cruising back to the decoys. The best thing to learn is how to set up the blind quickly and with as little noise, and you can get in pretty close. The am is the most sensitive, if you aren't sure where the birds roosted then I wouldn't push it.