you shouldnt transplant them until your root system is well established and healthy... no certain date, but you should either consider vegging with jiffy pots for the fact that once the root system has established you can place the jiffy pot with the plant inside a larger pot for transplant since the jiffy pot will break down into the soil itself over time. the other solution is to use a pot that the plant can grow in for its entire life cycle. that no no transplanting is needed