Okay well I'm going to take you through a train of thought here, and you let me know what you think...
If I were to say 48 hours of darkness, by what mechanism and to what result would that improve your harvest? If it's an improvement surely it can be measured?
Now if 48 hours did that, why not 72?
Why not a week?
Why not two?
Why not shut off the lights after veg?