I don't think that the plants are all that sensitive. Last year I bought 5 clones from a nursery that had them on 24/0. I brought them home and immediately put them on an 18/6 schedule. Didn't affect them at at. Then a month later, I hardened them off for about a week and during that time adjusted the lights from 18/6 to 15/9, then put them outside to stay. This was about last week of May. They didn't start flowering until early July (except for Blueberry Muffin which started about 6/20 - but even the nursery said this strain sometimes flowers early).
I have a theory (that's not backed by any data whatsoever) - when you put your plants outside for the first time, they are receiving so much more light intensity during the daylight, that longer night periods probably don't matter. Once they are fully acclimated to the outdoors, then a drop in daylight will trigger the flowers. (Just my thoughts, I could be completely wrong).
I think you'll probably be ok with your current seedlings.