Best Way to Initiate Flowering

I have some plants vegging at 18/6 light schedule, going on a 7am and off at 1am.

I want to start flowering them and I read in Jorge Cervantes' Grow Bible that it is good to give them a solid 36 hours of darkness.

I want to have the lights on during the cool of night for flowering though, so would it be ok to make it 43 hours of darkness, so I can turn the lights on at 8pm, or would it be better to do only 19 hours of darkness and start flowering them a day earlier?

I have read the same and tryed it many times with different strains, one plant straight into 12/12 and the other I would give the 36 hr dark, well I never seen any difference that would want me to pursue this method.
I just take them from veg and set them in flower. WHen the lights go off for 12/ then back on 12/ they will start doing what they are programed to do.