Mixing Protein Shakes

Question… After a Protein Shake is mixed, wheather it be Surge, or Low-Carb Grow!, how long will it be stable in liquid before it starts to lose its potency? I know this has been asked and answered many times, but I do searches and seem to get a ton of different answers from 30 minutes, all the way up to 8 hours. Can anyone shed any light on this? For the record, this is not really an issue for me as I drink mine right away normally, just one that I would like to put in the ol memory bank incase I ever have to answer for a freind or someone I am training. Thanks guys!