Never noticed a difference related to lights on/off. Might be a good idea to take your cuts a day after a good heavy watering, the supple green growth is what kicks out the roots so make it as supple and green as possible if you will. That is just wild speculation though:)
I guess another important thing would be to not leave the cuttings exposed to air for long after you take them. Cut, straight into cloning solution, straight to the prepared medium. I have take a big pile of cuts and just left them out, then all got cloning solution, then all into the medium. I was less successful doing that, only thing I can attribute it to was leaving the cut ends exposed to air for longer than normal. Now I try and minimize that and get the cut tip into its final home as quickly as possible.