Ezzjaybruh is right, what no one seems to have mentioned yet is that all cannabis plants have a preflower stage. For autos that lasts about 1 week, for photos about 2, for fast flowers? I would guess somewhere in between. You don't usually notice much difference at all for the first couple of weeks. The first sign I have noticed is a slight yellowing to all the new growth. It's still green but brighter, within 1-2 weeks following this, pistils will start popping out all over. 1-2 more weeks and frost will appear. :D