That's an awfully big amount of light in the middle though, not sure how it would work. You could try a 9/4.5/6/4.5 cycle and see how that works. You want the plants to keep vegging when they go out at 11 hours of light right? So that means you need to add 6 hours of light.

ANyway I hope that helps, let me know how it works out. I would make sure they get a good 15 hours of light a day though to prevent flowering. If they are getting 9 hours of light now you could either suppliment 6 hours of light at the end of the day, or try interupting them for 6 hours in the middle of the night.

When you put plants outside and the light cycle decreases instead of increases (like going from 18 hrs indoor to outside in early June when the days are still 14.5 hours long) they are more prone to flower.

he idea is to make sure that the TOTAL amount of light is never more than the maximum amount of light they will get on the longest day of the year. The MAIN cycle needs to be equal to, or less than the amount of light they get once they go outside. This way when they go out, the amount of light they get on the main cycle goes UP, instead of down.