I'm only activating half of the batch I just mixed. The other half will live in 32 gallon trash cans in the basement until needed.
I pretty much do the same thing. I have used Super Soil as old as 6 or 7 months with no problems just keep the soil moist with some R/O water and you should be fine.
R/O water? Shit, up here in Montana we just dunk a bucket in the pond. You must be a city boy.