I use to mix a protein drink before bed and leave it in the fridge to drink first thing in the morning or if I got up in the middle of the night. All I can say is don't do it if you don't have too! Bacteria formed on the top and it was nasty! And this was within 4-6 hours. I'd hate to see what it would look like and smell like after about 12 hours! So I would suggest not pre-mixing your protein drinks. There is no hassle with a blender or just get yourself a shaker cup for $2 from the grocery store. If I'm at work, I just add water to the protein powder already pre-scooped in my shaker bottle and shake away and drink.