There are revisions to the one-transistor timer schematic; as far as I know the original unmodified schematic is correct as posted by Tinhorn. Here's a link to a bigger version that'll just about fill a page if you print it:
Jon, I believe that I am correct in this, but just wanted to be sure. Unless you want to use the photo resistor for some purpose, you can cut R22 & 23 out of the circuit with no affect on the overall operation of the PIR. Am I correct?
Hi, Butch. Right... which is exactly what I did on mine. The R23 and R24 spots make good hookup points for the little one-transistor timer that GAntley and I came up with. In fact, if you compare the original schematic to the timer one, you'll see that I basically stuck those components right in place of R22/23/24.
In the last MS20 I modified I left the LDR (R22) in place, because with at DPDT center-off switch, one diode, one resistor, and the LDR that's in place (with minor circuit trace modification), I made a DAY/NIGHT/BOTH switch that seems to work pretty well for me. It does use between 10 and 20 microamps when it's in DAY or NIGHT mode, though (which probably isn't too much if you need the functionality). I haven't had time to write it up yet because I have another project in the works.