It depends on the strain and how sexually mature the plant is when you flip. I've had them flower anywhere from 5-21 days. How long have you been vegging? Are the newest nodes symmetrical or staggered? Do you see any little hairs?
The transition period is different for different strains, and definitely longer for long running sativa plants. Typically for hybrids it takes about 7 days to transition from veg to bloom, and the long ones tend to run 10 or 11 days after the flip.