Are they auto-flowering strains? If so, reducing the light hours likely won't help. But if they're photoperiod plants, yes you could get them to mature a little faster by reducing the light hours. I would still try to fix the problem too, as it's not a magic cure, and there could still be weeks to go. I still see nearly all white pistils on your plants, so I'd guess they have 3-4+ more weeks to go before peak potency. That technique is most effective on long-flowering Sativa strains, and has less of an effect on short or indica strains on average. I only say anything because your plant does appear to be more of an Indica strain.
What have been your watering habits? Is it possible you've been overwatering your plants? Also, is it still really hot with low humidity in the grow space, or have you been able to get the temps under control?