Summer solstice - 15 hrs of daylight
Autumn equinox - 12 hours of daylight
Winter solstice - 9 hours of daylight
I first noticed the spike nubbin right at the autumn equinox. Maybe the three-hour decrease in light is enough to get it going.
If we look at the same info for San Diego:
Summer solstice - 14 hrs of daylight
Autumn equinox - 12 hours of daylight
Winter solstice - 10 hours of daylight
Not a huge difference, so who knows.
I adjust watering to the plant, I don't force dormancy. In fact I'm still watering and fertilizing (albeit less frequently), but I'll stop once the plant has flowered its last spike of the season.
I have long wondered what the trigger is for dormancy (and for waking up). The species (and the ancestors of the hybrids) all come from relatively tropical latitudes where days and nights are pretty much the same length all year. It's rain that is seasonal. Somehow they are able to "anticipate" the end of the rainy season to start dormancy, and to "anticipate" the start of the rains to put out roots and new growth. Maybe humidity? Atmospheric pressure? I am curious...