How long is purchased compost tea good?

Purchased compost tea is probably worthless the moment you see it in the store. If it is in a sealed container it is not compost tea because it does not have active living microbes in it. How do I know? Because active living microbes generate carbon dioxide enough to burst the bottle. Or they will die trying (more likely). You have to have continual oxygen flowing to the microbes or they die. As soon as you enclose them, they are dieing fast.

On the other hand, if you get your tea directly from the compost tea brewing machine (see the Sanger General Store advertising (semilegally) on this site), then you can be pretty assured the tea is good for 12 hours and maybe more. Keep it agitated until you spray it out.