How long can you store gasoline in plastic cans before having to add stabilizers ?

I am just estimating but I would say 3 months but fall to spring is usually too long.

How long can you store gasoline in plastic cans before having to add stabilizers ?
Also, it will depend on how much air (oxygen) is in the container. A gallon of gas in a gallon container will last longer than a quart of gas in the same container

3 months is probably tops. If the gas MIGHT sit longer than 2 months, add the stabilizers when the gas is fresh. Stabilizers prevent, not reverse degradation.