Every year I grow my seedlings under 16 hours of light per day and they do well.
If you move some of them outside you need to harden them to outside conditions a little at a time so they can acclimate themselves to their new growing conditions.
i keep mine on 18/6 also and seem to get great results. they get a nice size before setting pods. its too hot right now for my babies to go outside, i have to wait a few more months. we dont really have winters here so i can go all year
Get'em out and let that intense sun-light penetrate thru the canopy. If you feel the need to use your lite's why not start another plant rotation indoors?