Indoor Veg Light Cycle

I am getting ready for my first outdoor grow. Currently, we are getting slightly more the 13 hrs of sunlight per day.

I want to veg my seedlings indoor til the mid to latter part of May before transplanting outdoors. What would be a good light cycle ... would 18 hrs lights on / 6 hrs lights off work?

I am concerned the natural light cycle -
13 1/2 hrs daylight with 10 1/2 hrs night might be too close to 12 / 12 and induce flowering when I transplant them outdoors.

Thoughts / suggestions / feedback appreciated.

In may there will be hrs of light. Keep your babies light on 24/7 or 18/6 take your pick.