Temperature drop to initiate flowering

[FinnBar]

how long of a period with cooler nights is needed to initiate flowering?

the only way i can achieve a good temp.drop now is messing with the central heating and a window ajar. since the outside temperatures went freezing it's become quite a handful to control it all "manually" (getting up at night and so on..)

will my phals get the hint in 2-3 weeks or do i continue with my new nightly routines until i see a spike?