You should be able to edit your post. I forget the time limit, but it is at least several hours and may be more than a day.
I will edit this one to check functionality.
just tried an immediate edit prior to posting. Click on preview post. Make your changes in the field below your preview, and then click submit reply.
Then click on edit in the lower right corner of your posted reply. Make your changes. Then either click on save changes or click on preview changes and make further edits.
Finally click on save changes.
I just did all of the above and it works.
When the edit link no longer appears on your posted reply, then it is no longer possible. The best you can do is make another post and refer to your previous one. If the thread is lengthy, you might state the number of the post to which you are referring.
Hope this helps.