well, Im going to give you no good answer. try it out, see if it keeps its mix, or if it falls/unmixes over the time of your workout.

I do not think there is a lifespan of protein in liquid. They do make RTD's, ready to drinks, and they have a shelflife of 1yr or so.

I would say, just try to work your muscles more with the shaker cup, or get a good shaker. Shake that thing up. I have the Bulk Nutrition shakers, 5 or 6 of um, They work real well. Sometimes my oats will settle after a minute or so, so Ill just stir it around.

I think it would also be easier to keep it as adding water afterwards so you dont spill and make a mess. If the spout comes off, It wouldnt be fun.