It depends, it can be as quick as a couple hours or it can take a day or two. But in any case if you're worrying about entering the challenge on time, don't worry about that: the mods seem to always go through the submissions right before the end of each challenge. :)

How long will it take? It gives me the impression that it will take me several days to accept the work.

It was not on purpose, it was a mistake! Worry not though, your submission being accepted or not doesn't depend on me clicking yes or no, ultimately it's the moderators who choose I think.

If I were you though, just to be sure I'd change that preview image to avoid it being rejected a second time :)

u clicked on no? u_u sad, I want you to accept my publication to participate in the challenge

Definitely better and more readable! Though I clicked on "no" because I didn't see you had changed it at first bc your preview file is still the same ToT