I find with more sativa dominant varieties 48 hours dark does push them into flower a little quicker than just going straight to 12/12, but more importantly they tend not to stretch so much in the first weeks of flower.
Just my experience tho and I have heard that this practice can stress your plants into becoming a little on the hermie side, never happened to me tho.
Try it you might like it
![Wink ;-) ;-)](/styles/smilies/icon_wink.gif)
or if your cautious like me then give half your plants the shock treatment and half not, that way if the worse happens you can only go half wrong.