2 functions I cannot find

a) Look for an “expire” plugin, there’s several of them, like this one.
b) I cannot imagine that nobody never made something like this, but I can’t find any such plugin. Perhaps with some simple coding. Anyone?

As far as authors, you could just use a lot of the code from an author template. Have a look at these:
https://codex.www.ads-software.com/Author_Templates
https://codex.www.ads-software.com/Template_Tags/wp_list_authors

And when you say avatars, I’m assuming you mean gravatars? Once you get their e-mail address, you can generate the gravatar like so:

https://en.gravatar.com/site/implement/php

Great – authors problem solved then ??
But still these putting posts on and off in time seams really problematic – it shouldn’t be so hard to do this.
All the plugins I found are either to ONLY delete posts or ONLY activate posts. And all is really complicated :/