That is the normal sequence of style sheets if you have a child theme.

However, I don’t really believe what you’ve been told to do to create a sub-directory inside a theme directory could be correct. It is against all known good practice when creating WordPress plugins and themes.

The main, and critical issue, is that as soon as you update the theme, all those changes in the plugins sub-directory will be deleted because the process for updating a theme or plugin will clear the previous directory. The normal practice for plugins and themes that need to create permanent auxiliary files it to put them elsewhere in the /wp-content directory. One common place is in the /uploads directory – as you can see in the third css file in your example: /wp-content/uploads/weaverii-subthemes/style-weaverii.css. That file is the CSS file generated by Weaver II based on the theme options you’ve set.

So, you better contact the plugin authors to find out where to put your when.php file so that it won’t simply disappear, or require you to manually re-create it everytime you update the theme. And even though Weaver II is not being updated often, the newest WP 4.3 required an important compatibility update, so Weaver II was just updated this week.