Coconut oil is almost fully saturated, so it has a longer shelf life than a *******, as it lacks oxidation sites (unlike olive oil for example).
Oil stored cold will last from months to years, depending on how saturated it is. Once heated, it will go rancid in a matter of from days, to months, again depending on the level of saturation, but also on the amount of oxygen available.
Corn popped in coconut oil should probably be fine for a week or more without going rancid. If sealed in a metallized oxygen-barrier bag, with a nitrogen flushing (like they do for Doritos, or any popped corn you get in the store), that could probably be extended to a few months.
I happen to pop using olive oil (the cheapest kind available is better than any specialty olive oil for this purpose; anything EV is awful for popping). Even olive oil popped corn won't go rancid for at least a few days, but for me, it's like finding out how many licks it takes to get to the center of a Tootsie Pop. I've never had it last that long.
I have a 6 ounce kettle. I make one kettle's worth, we eat what we want, and what's left over goes into zip-loc bags and into the kid's lunches the following day.
What I have found though, is that the humidity in the summer makes popped corn left in the machine overnight too soggy to be good. In the winter, that's not an issue, but in the summer, leftovers get sealed in a bag right away.
Speaking of humidity, remember to always leave the doors open while popping. It lets the steam out of the machine, and everything stays crisper.
