correction:
> The result I'm expecting for the above to be
>
> notification_time | finished_time | actual
> ------------------------+------------------------+-----------------
> 2007-07-06 15:50:00+10 | 2007-07-09 07:10:00+10 | 01:20:00
> 2007-07-07 12:30:00+10 | 2007-07-09 07:20:00+10 | 00:20:00