Thank you for writing.

Fertilizer pellets last about 9 months after potting but in a bag, without water, the nutrients have no way to leave the soil.  I would only fertilize if the potted plants did not grow properly.
Many people add too much nitrogen which can cause plants to shift from flowers and fruits to simply have a lot of leaves.

If it is really  important, you could put the potting soil in your garden or windowboxes.

I hope this helps.