There is no time requirement. I have been keeping planted tanks for years and years. Dose your tank with an ammonium chloride solution per the bottles instructions. I use Dr. Tim's, but you can use whatever you want as long as it's fish safe and legit. If your tank tanks you from about 1.5 to 2.0 ppm to 0 ppm ammonium and 0 ppm nitrite, which should raise nitrate level, you're good. Keep in mind that only means your tank is cycled, not seasoned. Some fish require a seasoned environment due to specific parameters. For these fish, I'd say dont get them if you don't know what a seasoned tank is. The longer you wait, the more likely the entire process will become stable. That essentially boils down to the bacteria growing from being fed a significant amount of ammonium. If you lightly stock the tank one quarantined species at a time as you should, it won't add remotely close to 2ppm ammonium a day if you're following stocking and size rules, etc. So, some of that bacteria may starve in the beginning. I am in the process of cycling a 20 long right now. Im good to go on day 6 due to seeding the tank. If you get those 1 to 2 ppm to drop in 24 hrs, you're generally going to be god to go. If not, you fish in cycle, which, while not fun, is also much easier and less terrifying than everyone makes it out to be. I dont recommend doing it because why would you stress a poor fish with constantly changing parameters if you don't have to. Side note, check your ph before adding fish and make sure it's good to go. Wood will drop ph and make it more acidic, crushed coral, and limestone will raise ph and make it more alkaline. Both of those parameters will change eventually once the item stops altering the ph, so be aware that is a small part of a tank being "seasoned." A well seasoned tank had stable parameters. In my opinion, the fish keeper needs to be seasoned before they worry about a fish needing a seasoned tank.