Flowering Question

I have three white widows that are flowering. I always counted the amount of time I've been flowering by going off of the day I switched the light over from 24 hour days to 12. For some reason I was wondering about whether or not that is right tonight. Do you go off the day you switch the light cycle or the day that you started seeing signs of flowers? I didn't get any flowers until day 10 after switching the cycle, so which way am I supposed to count?

For grower conversation purposes:...when you switch to 12/12.