You can absolutely have plants start to flower with only a couple hours of darkness, if they've only had 24 hours of light. I would start really small with 15 minutes of darkness at first, for at least a few days. You could also have a weak light on during the dark cycle at first, just to help minimize the stress. I had a bunch of early outdoor seedlings under 24 hours of light and they flowered when I turned lights off to spray for a few hours. Only 3 hours of darkness, 3 times in one week. Plants closest to the T5 didn't flower but everything except my indoor, did. The rest I have been cutting an hour off the light cycle every 4 days, still had some plants flower and plenty that haven't and I'm down to 17 hours of light. My indoor varieties which have been around for awhile and previously have experienced dark cycles, were unaffected by turning lights out to spray. Re-veg outside, means losing precious veg time.
