Some strains resist flowering till photo period starts at less than 12 hours light per day.
I go from 18/6 straight to 12/12. Have never messed-around with extended dark period in between the two. Guess I don't feel the extra stress is worth a day of quicker sexual expression.

Going from a veg light that's constantly on, to a flowering spectrum on a 12/12 schedule is usually enough of a signal to the plant that it's time to strut her stuff.

Have heard the fairy tale of bigger buds grown on a schedule of less than 12 hrs light a day, but have never seen proof. Kinda hard to wrap my head around the premise, that 7 hours of extra darkness will provide more energy to help her grow. Matter of fact, wouldn't it make her stretch more...?
Especially as the lady fills-in, I would think the plant would respond more vigorously with the 'extra' energy. (light)