With filters it's actually not necessary to change out the media, just swish it around in old tank water once a month to remove solids but otherwise they're fine to keep until they physically start falling apart. Your beneficial bacteria lives on your filter (and other surfaces in the tank, but the filter is the primary spot). If you're just replacing the carbon that's fine ^^ though the carbon is actually not all that necessary either, it mainly just keeps the water itself more visibly clear and after about a week loses most effectiveness at that and just becomes more surface area for the BB.
When you REALLY need to replace the pad, put a new one in alongside the old one for 3-4 weeks (imo) to allow the old one to help colonize the new filter pad.
Just for future reference :) keep a close eye on your parameters for a little bit to make sure the cycle stays solid 👍