Anytime a post is edited, the original time does not change. However, in the 'Replies' section it moves the post up to the current time that it is edited. This indicates that a post has been edited.
Your post fell inbetween two replies of 8pm and 9pm. This means that your post was edited.
In this case, you will not be the winner for this Challenge anyway so there should not be any issues.
However, in the future if any posts are edited after the closeout time they will be disqualified. We hope this clears things up and thank you for your understanding in this matter.