data about the rate of nutrient decay in fruit/vegetable juice
I decided to look into this question out of personal curiosity and here is what I found:

Some nutrients will naturally decay over time - mainly due to oxidation, but also on their own. The lifespan of most vitamins I looked up was at least a few days, so if you are making your juice ~18 hours ahead of time I doubt you'll lose much (if any) nutritional value. 

According to this article: http://www.ultimatecitrus.com/vitaminc.html


  When fresh citrus is stored at 38°F for 12 weeks, there was no loss of vitamin C, but when stored at high temperatures, the loss was great.


Vitamin A, B6, K also last for a very long time before decaying. Only a few have a low half-life, eg. B3 with a half-life of 20-45 mins, but your body can produce that on its own.

Based on that, it doesn't seem like you have anything to lose by making the juice in advance and storing it. If you were leaving the juice to sit in the fridge for weeks at a time then I'd say you might lose a tiny bit of nutrients (also the juice would go bad :-P).

A good tip is to minimize the exposure to oxygen by using either a sealable container or a jug with a lid that closes, and keep your juice in the fridge and the loss of nutrients is sure to be minimal even after the length of time that you plan to store it for.