Hi! Oh man, the cb advanced can be really tricky. I believe it says start CD 7 for a 27-29 day cycle. I'd start there, if not CD 8. The reason why, is that one day makes a huge difference. I have PCOS, so my estrogen surge and my lh surge can vary cycle to cycle. I actually keep the holders and use them repeated so I can start them on different days. Once you read high estrogen, it will continue to read high until you get a peak. So I suggest following up with a cheap opk like Wondfo where you can test more often or even stop testing once you get a high until you get a positive.
For example, my last three cycles were 27, 26, and 26 days. So by the instructions I should start on CD 7.
The holder that I started on CD 7 read high on CD 8. My peak was CD 13. So I would have had 5 days of high readings.
The holder that I started on CD 8 because I know my hormones are weird/I get cycles up to 32 days read high on CD 12. So I only had one day of high reading.
Either way, I didn't ovulate until CD 15. So even if I had waited until CD 12 to start bding, then I would have been in my fertile window.
Being new to it, I'd say err on the earlier side but just know if you keep getting flashing days to not panic. It's also suggested to start doing opks 2-3x a day once you start flashing (I usually do fmu, afternoon, evening) which is another benefit to having the cheapies. The cb sticks are so expensive.
Sorry for the long winded answer! Lots of baby dust!
I will start testing this morning as on day 8 of cycle
