Expanding the date into a time-ago timestamp (client-side) makes sense. However, the username being included in the message and the phrasing of the message itself ("edited" vs. "modified"), should not differ from what the server generates. The user information is available server-side at no extra cost and tied to the same revision with regards to caching.
I'm also curious why the flash is happening at all (tested in Chrome 42 on MacBook Pro 15" Retina, using https://en.m.wikipedia.org/wiki/Kahl%C3%BAa as example) as the relevant code is loaded from the `<head>`, and called from an inline event:
```
<a id="mw-mf-last-modified" data-timestamp="1423188925" href="/wiki/Special:History/Kahl%C3%BAa" data-user-name="ArturZ72" data-user-gender="unknown" class="last-modified-bar truncated-text">
Last modified on 6 February 2015, at 04:15</a><script>
if ( window.mw && mw.mobileFrontend ) { mw.mobileFrontend.emit( 'history-link-loaded' ); }
</script>
```