Thanks for all the responses, and the useful links.
My camera is a sx260hs. Running get_propset returns a value of 5, which I see is not on the
http://chdk.wikia.com/wiki/PropertyCase page. I can go through the settings and add that in sometime over the next few weeks.
I have a setting called Power Saving->Display Off which has values of 10s, 20s, 30s, etc. Using
http://chdk.wikia.com/wiki/PropertyCaseDump doesn't show any differences on properties 0 to 400. Is there somewhere else that this information could be stored?
On another topic, I ran some tests on set_resolution and found the following:
set_resolution 0 = 4000x3000
set_resolution 1 = 2816x2112
set_resolution 2 = 1600x1200
set_resolution 3 = XXX
set_resolution 4 = 640x480
set_resolution 5 = XXX
set_resolution 6 = XXX
set_resolution 7 = 1984x1488
Where 'XXX' appears to crash the camera.