Photoperiod - what is the appropriate 'winter'?

[rockyfarm]

Growing under lights, it is feasible to control intensity and duration (and, of course, temperature and humidity, as well as nutrient supplies). One can reduce winter (cooler, dryer, shorter days) to the minimum needed to initiate bud formation or dormancy requirements for those orchids with seasonal cycles. AOS publications suggest a 'several month' duration of shorter photoperiod for mixed collections or sensitive plants. My question is: what is the minimum time for this winter break? I'd rather see my plants growing fast, rather than idling in the cold and dark. Has anyone reduced winter to one month with success (for photoperiod sensitive orchids)?