Looking real nice, Now's the time to kick up to dual spectra!!! The onset of flowering between days 18 - 28 are right on par. Now is the time to give them all you can (but not over doing it) to let them be the most they can be!
I have found most autos don't like overwatering, I let the soil dry out in between waterings so it is not always "wet" looking. I really like to use the "pick-up weight" to determine when to water. Feel the weight of a dry pot, then water it thoroughly and note the feel of the weight of the wet pot. A simple
Soil Moisture Meter from the garden shop helps too.
For a "feeding", water with enough solution that about 15 - 20% of the volume runs from the drain holes. Let the pots set in the standing water for about 5 minutes to be sure the root mass is saturated with no dry pockets, then discard the remaining water.
For watering in between feedings, when a pot begins to feel "light" add in your water 1 l or qt at a time, slowly, until you see water begin to trickle from the drain holes.