I think you can delete your personal posts on threads after 24 hours but cannot delete a thread you create yourself and that’s what I thought he meant.
It all depends on the subforum where the post was made. In some boards, you need to wait 24 hours before you can delete a post. So, you are right about that. But in others, you can immediately delete it after submission, and there is no need to wait.
OP, go to settings, reset your account password, but before you type the new password, kindly close your eye and type in different letters from your keyboard. Open your eyes after then and don't cross-check the letters, then submit it and walk away. That's a way of forgetting about your account if you don't actually want to gain access to it.
This request isn't about OP losing access to their account and not having a way to log back in to use it. They wanted to have their posts and history cleared due to, what they believe, is sensitive content and information they posted about taxes.