Depends on how long the plants have been growing and what strain it is. From my limited outdoor growing experience in South Eastern Australia many years ago. I planted a sativa strain in September and it wasn't finished until May or June the next year. And it was massive. I planted indica strains in Jan and they were done by May.
My guess is most strains won't flower until you start getting closer to 12 hours of daylight. Although I could be wrong.