I may be wrong but I'm assuming that they are pelargoniums in which case I would just let them have their way and when the temperature drops to near freezing then deal with them as you mention. I see no reason why they should be forced into a particular length of rest period.

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MS.....it is always hard to decide when to force our plants into dormancy by removing their bloom.

The weather most often dictates our decision. Left too long in their pots, a killing frost overnight can do harm we'll be kicking ourselves for....yet as long as the daytime temperatures remain mild, there is really no reason to deny the plant's going on.

For this you might just take the plant into your garage during nighttime when the temps get down where we think they might affect....then take them back out into the sunshine during daytime hours.

But, sooner or later, the decision is to remove the bloom, remove them from their pots, allow them to dry for a day or so in the garage, then taken to that cool room where they remain untouched until mid February when we bring them back out, cut back, and re-pot them, given good sunlght and in about 6 weeks or so, much new foliage returns.

If theyte pelargoniums well, I dont give them any special treatement in winter indoors, other than pruning them back hard.
In fact they will just keep going if you let them(tho they will get legy with less light)