I joined on November 30, 2021. I'm pretty sure it's already been a week since I've been here (11-30-2021-12-07-2021) and yet I STILL can't post anything. Do I have to wait until it's been EXACTLY 1 week since I've been here, regardless of what time I joined?

My guess would be that yes, you do have to wait until it's been exactly a week. If you're still not able to post tomorrow, you could try contacting an admin about it.