Morning...for a couple reasons.

1. You can set up significantly ahead of time without having to worry about spooking deer as they are typically out in the fields feeding.

2. After shooting the animal you do not have to worry about trailing it in the dark.

3. As the morning progresses you stand somewhat of a better chance if there are other hunters out there moving through the general area.

4. You have more time to process the animal immediately following the kill in warmer weather.