Ive heard a lot of different opinions on this but does anyone know for a fact that a 24 hour dark period before flowering actually helps?
I'm a bit confused. Are you saying on Day X you have 24/0 lighting; Day X+1 you have 0/0 lighting; Day X+2 you have 12/12? If so, I think I read in one of the growing books that the author had heard of it, but personal experience had not yielded signifigant change. My personal opinion is that when we grow indoors, we should control lighting perfectly to make the plant as stress-free as possible. I would just go from 24/0 to 12/12 like normal, but that's just me.
I usually give about 30-36 hours dark between veg and flower, partly to "kick-start" the hormonal reaction of flowering (which is not a universally accepted claim) but also partly just to get my flowering light cycle onto my personal clock I have to move around the lights-on time. Giving the plant a shot of dark between veg and flower won't hurt it, I do acknowledge that it is questionable if it helps at all.