Yes, the flowering time Days start when you switch to 12/12.
And there is no need for debate. If it is a 100% sativa, the flowering time will be
at least 12 weeks, probably 14-15.
If that is the case, then your plants are right on schedule. Using the 40/60 Theory, when the plants stop stretching, you are 40 percent of the way through flowering. The other 60 percent is flower formation, and flower ripening.
HTH
