I don't think you can use the indoor finishing time for a given strain to estimate its outdoor time, for example saying a 9 week indoor strain will finish outdoors 9 weeks after the first flowers form.
Indoors the cycle goes straight from a 18/6 or 24/0 veg cycle to a 12/12 cycle, and finish times are figured from the start of this cycle.
Outdoors the plant endures a light cycle that slowly changes from 15-18 hours(depending on your latitude) on the longest day of the year, towards whatever length of day triggers bloom in mid-late summer. There is no slamming straight into blooming, it develops slowly at first, and would be very hard to judge.
Indoors the cycle goes straight from a 18/6 or 24/0 veg cycle to a 12/12 cycle, and finish times are figured from the start of this cycle.
Outdoors the plant endures a light cycle that slowly changes from 15-18 hours(depending on your latitude) on the longest day of the year, towards whatever length of day triggers bloom in mid-late summer. There is no slamming straight into blooming, it develops slowly at first, and would be very hard to judge.