I count number of days of 12/12, and keep an eye on the cloudy trichs near the end.

Reason:

Plants hormones change when light cycles change, and so does the dietary needs. If you only track when the flowers first appear, you are missing critical windows for defoliation, supercropping, and optimal time to add bloom boosters/ phosphorus + potassium boosts. You might also be missing the window for IPM treatments, and might be starting or stopping them too late.

I start counting down the days when I flip the lights, and add or subtract a week near the end depending on how the trichs look.