it depends on individual system... for my case, i used 60-70 kg of cured LR (cured in an old tank for a month) and didnt experience any cycle at all. One day after adding LR, no NH4 or NO2 detected. Added a market prawn for 4-5 days.. again, no NH4 and NO2 detected.. i waited for another week before adding any LS... As suggested, best is to use a testkit..