I have used a lighting schedule for a couple grows now that seems to actually help the yield. Lower the light 2 hours just before harvest making it 10-14. It increased the size of the buds compared to the grow before. I'm not sure if 3 days is enough, I usually do it 10 days prior to harvest. But what I'm taking a long time to say is that, no, you won't have any problems. Especially for that short of a period of time. So go ahead and change the lighting schedule to either keep it the same time on but change WHEN it comes on by an hour, or just turn your lights on to water then go back to your normal on-off timing. A single time doing this, and this close to harvest shouldn't stress them very badly at all.