The specs say that the
datetime attribute on an
del tag should be in a standard UTC format. The
+00:00 means that the datetime is in Greenwich Mean Time. So, in short, it is using the "correct time," in a format that is unambiguous and universally correct. (That is, the actual time when you click the button and to make the insert.)
Edit: Of course, the argument could be made that it ought to tell the actual time zone that you're in, and enter the
datetime with that time zone. After all, that tells someone whether it was late at night or early in the morning when you posted the change, as well as the actual moment in time that you made the change.
But, from an HTML point of view, it is telling the time "accurately," in the sense that it's referring to the correct moment.