There is no time period for cycle, you should look for an amonia spike followed by nitrite spike (amonia will go down), until both are 0, don't settle for anything less than that, after both value are 0, 20%-25% water change and you are ready to start, start means 2-3 fish, wait 3-4 weeks, and same number again, let the bacteria population build up gradually, slow is fast.., patience is key