Hi Shaun,
I've uploaded a flowgraph to my blog that shows an example of how you
could decrease the players health constantly during the night.
http://1.bp.blogspot.com/-3203hTMEYUM/TmhJRRtVhEI/AAAAAAAAAIc/gkndJb4NeE8/s1600/CauseDamageAtNight.JPG
The example takes off one unit of health each second between 6pm and
6am.
This will eventally kill the player so you might need to tweak it to
either take less health off or take it off more gradually.
The problem you have with only temporarily taking health off, is the
players nano suit will automatically heal the player. A way around
this is to change the player model so it no longer has a nano suit.
This link will give you a tutorial from a previous course showing how
to do this:
http://arch1101-2010jc.blogspot.com/2010/06/changing-player-character.html
Alternatively you can use the Nanosuit:Nanosuit flowgraph node to set
the energy level for particular times so that the player wont heal
themselves.
Cheers
Jules