Thanks, Thomas.
However, it doesn't seem to work; I assume that's because the minus
operator has trouble working with times!?
If I did it right, then it isn't minusing times, it's minusing
integers (seconds since the epoch). I'll go do some testing...
...
It seems to work fine to me, however it isn't particularly useful due
to caching. Add ?action=purge to the end of the url when viewing it,
and it works just fine. You would need to turn of caching for it to
work properly.