I'd venture to say when they're up feeding...to or from the food source.

Pure "guestiment"' here, but I would venture to say that hunting the water hole in the afternoon/evening would probably be better, after deer are moving from bed to food source. The early season (here anyway) is the end of the dry season, and still very warm. A water source along a whitetails transition area from bed to food or vice versa could be a great strategy. The situation/geography/environment are all factors though.

Just take a seat in the morning and evenings, then make your judgement.

Good luck.