What kind of soil ? Does it have nutes designed for cannabis in the soil ? If so just plant them in the pots & you will only need water pH'd to 6.3 for the first 2-3 weeks. Then you will need to add nutes after that. Fox Farms Ocean Forest is my soil of choice.
You can feed MC as soon as you pot the plant. I start at 1 gr. per gal. & increase a gr. per week till I get to 4 gr. After that I go up .5 gr. at a time.