It has nothing to do with temps.
Light leaks during the dark period will prevent flowering, not encourage it.
Cannabis will grow primordia/pre-flowers at the stem/leaf junction once they are old enough, this is known as "sexual differentation" and this can happen at 18/6 but does not mean the plants are actually flowering, they have just reached "puberty".
Flowering will only commence after changing the light cycle and your plant should keep growing as usual without flowering even though there are primordia popping up all over and you still have the lights at 18/6.
Be careful though, light leaks when she is flowering under 12/12 can cause hermaphrodites, so you will have to address this before you go to 12/12.
If they do indeed flower at 18/6, then you do have autos and not photoperiod plants.
Hope this helps, Organoman.