Did you wait until June?
I'm in a similar situation. I'm running 18/5 light cycle and planning to reduce the daylight cycle by 30 minutes a week until I'm at 13/11 and then put the plants outside mid spring. I'm hoping if I do it gradually half an hour per week instead of a big jump from 18-13 then the plant might stay in veg. Also the plants are unfeminised so if they did show signs of going into flower in this period it might help me to work out which ones are female and which are male. Just interested to hear what you did and how it went for you?