Most Dendrobiums like to rest a bit and dry out at the roots in the winter, but if you see active growth then you can water more frequently even in the winter. Generally, they also like a cooler period in the winter and can handle lows into the 50's. I would definitely not keep the block of coconut husk it is in very wet at all unless there is a new/active growth. This is a sure recipe for root rot. Those chunks of coconut hold a lot of water and do not dry out very fast.
I'm not sure about Brassia 'Bill Switzer' but I know Brassia Rex Sakata and Brassia Eternal Wind Sato both like to dry out more at the roots in the winter as well especially if exposed to cooler temperatures, unless in active growth. With my Sakata I withhold water other than misting a bit until I see the new growth, which just started about a month ago, and now I'm watering 1-2x/week to support the growth.
Hope this helps a bit?
Matt
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