Some of mine seem to want to hang onto their leaves regardless of what's going on outside. Warm or cold...some just seem to need the push to move in that direction by a reduction in watering. And, yes, I always have a few that need a push to move toward dormancy.
I typically being reducing water in late Oct/Nov...except for seedlings. If the plant is mature and the growths have matured sufficiently then I first start letting them go dry between waterings and as time goes on I increase the length of time they are allowed to be dry. By late December I am barely giving them much water all all. A little "sip" about once a week or so.
One little issue I have due to the dryness of the lights is that the sticky sap of the flowers in this group can become a problem so even if I'm not watering the plant much, I do take them to the sink (about once a week-10 days) and rinse off the buds carefully w/tepid water. I find I'm losing less buds since I started dong this. Plus, I try to rinse the leaves and it helps get rid of some of the sappiness that comes w/those as they age. I've even been known to wash the leaves w/some soapy water...again, being very careful not to soak the medium when I do this. It's helping w/my bud loss this time of the year. OR...maybe my buds are just doing better and my washing them isn't helping at all...and it's all in my head. But, at least I don't have sticky sap all over my floor and shelves like I have in previous years. And, I haven't been losing as many buds this year.
Back to watering...my HO T5's are very drying so I will continue to drizzle water around the edges of the pots (or putting a little water in the bottom of the saucers) throughout the rest of the winter about every week or two. Be very careful when doing this (if you do) because some will rot if too much water is left to sit for long-ish period on the pbulbs. Some are more fussy than others about this. I water only enough to keep the pbulbs from shriveling too much. It works for me but I know some people who don't water at all until they see new green in the spring.
The small seedlings/compots I water through the winter w/no dormancy.