J.B.
You should start when it gives the high fertility reading and continue through your peak fertility readings, as well. Every other day is more then adequate to get the job done :)
I only used the CBE Monitor for 2 cycles- it didn't work for me just because my cycles were SO thrown off by a miscarriage a couple months prior. I have a friend, though, who got pregnant every time while using it.
I know it's easier said then done, but relax and just try to enjoy the process! I think I remember reading somewhere that it takes an average of 5 months to get pregnant? Any way, at the age of 23, it took me 4 months to get pregnant with my first son and at the age of 26, it took me 7 months with my second.
G/L and I hope you get your BFP soon!