most plants dont need 12/12 to start flowering usually they need somewhere between 10 -11 hours of dark period to start flowering so just pick an early flowering strain. or you may even try one of the autoflowering strains or autoflowering crosses veg them indoors to get them started and then place them outdoors.
you do not want to start flowering before you put them outdoors they will not continue to develop buds they will reveg and it will only set the plants back.