The cycle begins the day you flip the lights to 12/12. However many days/weeks you've had the lights at 12/12...that's how long you've been flowering.

Remember, most strains still show some variation, and something could have happened during your grow that slowed the flowering cycle a bit. If your plant strain is supposed to flower for 9 weeks, and you're on Day 72...it's unusual, but not *that* unusual.