Hmm... what kind of light? Is it shining directly on the plants, or is it reflected off a wall? How far does the light have to travel before reaching the plants? If you are inside the grow area, can you see your hand when it's dark?

If there are significant light leaks, then I would just veg 24/0 until the leaks get sealed up... then you can switch to 18/6 or 12/12.

I have not heard of light leaks during veg causing hermies (that would be your main concern I imagine) , but I would like to know if it has happened to someone...(?)