Hey Evil,
Yep, around Day 17 was when the plants started to take off, but I think the important part to any grow is building really strong roots early, and that starts from Day 1. To my mind, the roots are the base and foundation of growing a good plant.
I always take a look at my roots after I harvest and see how they developed and how they have had an effect on the plant.
If you are interested, take a look at a nutrient review I posted >>>
HERE <<< There are a lot of photographs of different plants I have grown and the root systems etc, it may help or at least give you some ideas.
I always grow in Auto pots now (they really changed the game for me). The biggest improvement I made to growing in soil. It gives me perfect watering and feeding 100% of the time.
I use Cana Pro soil with extra perlite and clay balls mixed in, but I also add in some "Charge" (a root developer) with a few other root additives as mentioned.
This grow I have only used my HPS light, a Lumatek 600W 400v Digital Dimmable Pro Balast, with a 600w Dual spectrum enhanced bulb. It is a super light, that really penetrates the canopy. I raise the lights through the grow to keep them above burning level. A little silicone added to the feed will help protect the plants against the higher Temps as well.
Managing Temp, Humidity, Airfolw, etc can be a fine balancing act, but get it right and things grow BIG. Not just Caramel, as you will see from the nutrient review photographs.
I just happened to hit upon a system that combined with a good nutrient range produces those results for me.
Hope that helps you a bit....