One problem that I've had in the past with making smoothies ahead of time is getting the right consistency because many smoothie recipes rely on ice or frozen fruit to thicken them and thus are not great after several hours in the refrigerator.

I found and have been been playing with a make-ahead recipe that includes oatmeal and chia seeds placed dry in the blender and processed to the consistency of flour to thicken the smoothie, which means you can make them ahead of time without sacrificing thickness. 

Recipe source: http://www.theyummylife.com/Oatmeal_Smoothies