It sounds like you have an auto. You have no control over when they are going to flower. I started to top one once, and I notice it starting to flowering. You don't need to top one after it starts flowering, just let it do it's thing. Make sure you have a regular plant that you can conrtol and make it flowering when you want to. 4 weeks to 6 weeks are all right for starting a new top from toping. then you can turn back you light's at 8 weeks, and start the flowering stage. Good luck, and happying growing.