Same thing, just sent in an email. My observation is stuttering begins around the first day/night cycle (within the first 5-10 minutes), and gets progressively worse with each continuing day/night cycle (every 12 minutes). After 2-3 in-game days, it's so bad that it resembles a continuous severe frame rate drop. The only fix I've found is to super quit and relaunch. But that only lasts for 5-10 minutes before the problem comes back.