Cloudy weather would be like putting the girls under flouros one day a week and turning off the HID, but on the SAME SCHEDULE.
The first day of darkness is a kick-start to signal flowering. It's actually supposed to be 2-4 days.
One 'off' schedule day will encourage hermies.
If you are going to run 10 hour light days, you must run ALL your days 10 hours. That is an advanced technique; there is a qay to speed flowering that way but you lose yiled. Remember the equation .5g/w/m has TIME as one variable; it is the time spent under flowering lamps on a flowering schedule.

Stick to 12/12 and be patient.