I modified Raoul's [tag]Simple Recent Comments[/tag] plugin a little as mentioned in this post.
I changed the display further such that number of hours elapsed is displayed instead of minutes. I have also fixed a flaw that negative time was shown. The time of the comment is taken from 'comment_date_gmt' and the value from php's time() is actually the server's time not UTC time. Therefore I have to add the difference between [tag]UTC[/tag]'s time and the local time of where the servers are.