Once the thread has been created, you have at least two hours to edit it.
The title of the thread can be edited as well. If you erase the title and leave it as is, then it will become a thread without a title.
I learned the trick when I submitted a duplicate thread. Before a MOD finds it, I usually change the original title to "Duplicate thread, please
delete". One time, one member did submit a duplicate, he erased the whole title and left it as is, a thread without a title.