Starting sativa seeds indoors in March and moving the plants outside in late May gives a long flowering strain the head start it needs in a northern summer. The catch is hardening off, because a plant that went straight from LEDs to full sun will bleach and stall for a fortnight. The transition schedule on https://hazesativaseeds.com spreads the move over a week of increasing outdoor hours, which sounds fussy but avoids the setback. Also watch for early flowering if you move them out before the days are long enough.