Curing magnesium deficiency

I estimate decent preflowers to be there in a couple of weeks time, which is why I suggested my schedule like that. I could be off slightly, but flowering time for these plants is supposed to be 48-56 days (depending of the strain). I'm not exactly sure from which point they measure this, on the seeds company website they say "your plants will grow a couple sets of leaves and will then start flowering", technically I could already be in that timeframe already.

Just to give one example I know of sensi NL auto has a flower time of 45-55 days. It takes about 85 days seed to harvest, most of what I have read suggests with most autos flowering doesn't really start for about 30 days. Different plants and phenos vary widely though which is why I would go by the preflowers.