Bleach does not stay effective for very long. I would not trust it past the day it was mixed. Also, don't forget that the bleach in the bottle you bought will not last forever once it is opened (meaning that you will need to use extra if the bottle is more than a few months old).
When you are using 1oz. per 5 gallons, there is not a lot of room for error in the concentration of bleach. Always best to use new solutions.