Timing between events

How would I see how much time passed between two (possibly identical) events? Like:

The sun rises.
(an unknown amount of time passes. other stuff happens. etc)
The sun sets behind the hills.

At this point I want to send the length of the day to the MUD. (in days, hours, minutes, seconds, if possible) The timers that I found seem to be for set intervals or times. I want to do the opposite and find the time that passed.

Thanks,

http://www.gammon.com.au/forum/bbshowpost.php?bbsubject_id=719

And actually, nick has a plugin:
http://www.gammon.com.au/forum/?bbsubject_id=3102
Its for 'leveling' but you can take the guts out (since it's probably more useful to you outside of a plugin) and tweak them to your needs.