I've never requested that a post be deleted, so I didn't even know there was a limit. Once I started a thread that I realized had already been addressed...I just did what marvin_pa suggested. I deleted what I'd typed to make the post blank, then filled it in with "mistake, sorry".

If you're referring to posts you've made on a thread that is already running, you can edit your post. If the time is past for you to edit....hmm. I guess that all I can offer is that you carefully consider what you want to say before you type out the post.