You can put it up anytime. There was no mention that the image had to be unpublished. I entered an existing gallery image for last weeks contestl

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi