I dealt mostly with WordPress, so PHP was already there. Wouldn't that make the date displayed dependent upon the client device? I figure something like that should be based on the server so it's universally set by the owner.
Discussion
Yes that's correct, it would use the browser/device time to render the date. With PHP it'll need to check server time and also could be shown as stale, if the site page caching was aggressive. The JS method is just more lightweight and works with static page and will "update" despite page caching.