As long as theres a blanket of co2 on your beer....a long time, months. I can go through a keg in a matter of weeks so not certain but as long as its not introduced to oxygen ya should be good for quite some time.
My plan was to just hook it up at 10-12 psi and let it sit. Try it after 7 or 8 days and leave it that way. So I guess if I keep it at 10-12psi it sounds like it should last a good while.