I've done this the past 2 cycles and while it's not set in stone, it's helped me go from 34--36 day cycles to 31 (same LP)
I blended regular unsulphured molasses with apple cider vinegar (1/3 cup molasses into 2/3 cup vinegar). Take 1 tbsp in the am and another in the pm, about 12 hours apart every day from CD 1 to past ovulation.
I can't believe how well this has worked for me. I was going to try the fish oil and evening primrose oil, but I couldn't take those consistently. Yes, it's kinda gross but you chase it with water after. The taste is gone in a few seconds. I think it's worth it!