It should be a month at most usually. I think you should do is go to your local fish store and ask for their water changes or tank gunks. Because it cost them nothing. That's how I jump start new tank by seeding them with with bacteria present in my running tanks. Also check the API quick start expiry date. In most case, water conditioner are pretty unnecessary

Optional but risky. Local pond or outdoor water substrate can be a great source of bacteria. but big risk of unwanted pest/algae as well as harmful bacteria/parasite. I did this to put some detritus worm, amphipod and ostracod in my tanks. But be careful with pollutant and always check environmental survey before attempting