Start them now , by now mid may you should have some nice 1’-1.5’ tall plants .
If you train them right they could already be in Bush shape.
STR8

depends how big you want your plants I guess... with that for lighting, you won't get too far though

I would think it possible to start them now, inside, under a CFL or some flouro tubes. Plants need to be above 15*C to grow well, so you can plant them out when the lowest temps are around the 15*C mark...you can get CFL's or flouro's close to the seedling...within a few inches.
You did not mention if the seeds are AF or PP... If they are AF [auto flower] then be aware th@ AF's do no like to have their roots disturbed so often dont respond well to repotting as a regular PP [photo periodic] plant would.

With PP seedlings, I suggest you pot them up into a larger pot every 2-3 weeks until you plant out...the idea being you grow the seedling to fill the pot with roots, pot up and grow it full of roots again, then pot up again. This give the plants time to build a strong and dense root system which will help them when they are planted out in the ground. If you just grow the seedling from the beginning in a bigger pot the root system will be much less dense and matted, possibly not even holding the rootball together.

Growing outside one faces a range of problems.

Grazing or curious animals: if these are a possibility, write out a list of potential animals and how each could be countered or treated...this might be beer traps for snails, noise traps to startle wildlife etc...
INSECT: these buggers WILL turn up...its Ma Nature and she can do as she wants, eh? Just be aware they often come in waves. Write list of potential bugs and the treatments for each. IF POSSIBLE, keep a range of 3 products and a sprayer onhand to spray the plants... suggest pyrethrin, neem and saposidal fatty acid soap and a liquid sulfur [for mold]. adding a little liquid seaweed [1/4-1/8 str] to the spray give the plant a light feed also.

Prepping the planting hole beforehand helps a lot if you can do it.

muA