HTML5 sidebar syntax
The aside element already creates a section, there is no need for an additional section element.

If you use h1 for the aside element’s heading, the headings in the article elements should be h2 instead of h3 (or also h1, but that’s not recommended).

But using article for these short snippets might not be a good idea in the first place (unless they will contain more than just a date and an image), because each article also creates a section.

For the date you should use the time element.