How long can I store a bag of Quikrete?
Depends on how exactly you store it. If you want to keep it around as long as possible without becoming a brick, put it in a seal-able plastic tub with desiccant packs and keep it in your house (as you said you were).

Too much effort in my opinion. Just take it back to the store, get your money back, and repurchase a new bag in the future when needed.

I've had bad experiences with them turning into bricks in a high-humidity basement; took about 6 months for it to happen.