You cannot smoke leaves. Well, you can, but its pointless. THC is formed in the flowering period. How long have you been growing your current plants? Whats the current light timing? Your very vague so its hard to help.
I really have no idea what you are asking friend. Do you mean how long before flowering? Please elaborate.
I'm sorry I haven't started growing yet( I'm germinating) like if my plant starts heading for worse before it flowers (like the leaves start turning yellow) then can I still harvest the leaves.
Don't even think like that. First off, don't smoke the leaves, it's pointless. Second of all... read these forums. Start through the beginner page, and work your way through. You will gain enough knowledge to have a successful grow, and your grows will be better every single time. Look at the link in my signature, then go to the last page (actually the 6th page). That was only my second grow, and I owe all my success to the knowledge I gained here, and a little bit of hard work.
I dont really see a point in harvesting leaves, but if they were to turn yellow or something, im sure you could solve the problem with some help from the city. Why worry about the plant getting sick, just grow it one step at a time, and hope no problems arise.