D, it will usually hold it's ability to discharge for a few days. However, what I've seen is, the time it's been exposed to the air has allowed enough possible clumping to happen that if you try to use it again a few days later, even with a good whipping, it may booger up on you in the screen making it more of a pain then a savings. I've just tried to narrow down how much to mix for a job, minimize waste, but in the same time not leaving myself short on enough of a custom color mix for the job. My advice, unless you plan on using it fast, don't bother.