I live in NY State and planted ~30 sunflower plants this year. I started them very early indoors so had early blooms - I've had seeds on the faded flower heads for ~ 4 weeks now. Is it possible to harvest the seeds, immediately plant them and have new plants sprout this year? Are the seeds viable or do they need to be dried further (or aged)? I have searched but haven't been able to find the answer to this particular question.
Based on this abstract Sunflower seeds are dormant at harvest time. They need a period of cold conditions to break this dormancy. It's a biological mechanism to prevent the plant from sprouting immediately and dying when winter comes before it can produce the next generation of seed. A few odd seeds may sprout, but they will be in the extreme minority.
Breaking Dormancy appears to take around 40-50 days based on this article.