Time of year: probably not one of the holidays because it will be very crowded. Time of day: definitely morning before it gets too hot and before any rain happens because central Florida gets rainy (especially in August). Again, also less crowded in the morning so better view of the animals.
Early if you want your$ worth
Evening seems to be a good time of day, now that that AK is open in the evening. Less sun = less heat, and Pandora is a different land in the dark.
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