@pdawggydawg - I moved your post to a new thread as the other was quite old. First, did you try any sterilization tactics? I'm no expert but I'm sure there's no set time. It likely depends on the severity of the issue.
It depends on the severity of butt burn. On some research animals, I found evidence of a secondary infection after death. It is possible for the animal to survive butt burn and regrow tissue. I would make sure your water is in pristine condition.