Light adjustments needed before placing outside

HIGH to everyone,
My 3 girls are one month old and growing slow but very healthy they are inside under CFL lights. The light schedule is currently 17/7, I plan on putting the girls outside in 16 days on June 6, at that time the day length outside will be 14.25 hrs.
My question is at what increments should I adjust the inside lights so the girls do not start to flower when they are placed outside in the garden?
Would a 30 minute reduction every three days stress the girls?

Thanks for the suggestions and help...

Ive been doing 1 hour every 2 weeks im at 15 hours atm cant see it realy stressing them out too much.+ they have all summer to "recover" if they do stress.

Thanks for the reply, I took a chance and placed them outside in the shade. I has been 2 days with no stress, only fast growth. I will place them in the ground in more 3 days.

I placed my starts in the garden a week ago. They had been in my veg tent on 18/6 for about 3 weeks from seed.
I just reduced my light hours to 15/9 to help them acclimate to the shorter day time for a week and put them out.
Absolutely zero issues. (other than friggin' bugs)