I've changed the date format to be a bit more SEO friendly. There's definitely room for improvement here, suggestions are highly welcome as usual.

We could say

Today

or

Yesterday

above the message, but that would be confusing to search engines.

When you hover over a message in a thread, you should see a corresponding date. It's helpful, but if messages of one user span across multiple days you wouldn't really know about that.

I think we should group user messages per day, so if my messages span across few days I would see my avatar multiple times.

We could also have some kind of a border between days, but I'm not sure if that's valuable. Grouping user messages per day might be good enough.

Oops, merged in threads by accident :).

No way to go back!

I'll try to implement the message drag and drop we discussed.