I dipped my foot in in December and it was still pretty warm!
I believe it is but chances are it won't need to be heated.
The pools are heated to 82 degrees year round at all of the wdw resorts.
No, the weather is still warm enough that it doesn't need to be. It's lovely just to cool down in the pool. There are a number of heated spa whirlpools around the pool areas if you need it. Having stayed now twice at Yacht and Beach this is the nicest pool area.
We were there in December and it was heated. Now that I read this I think you are asking when is it turned on...
Get an answer from Disney's Yacht Club Resort staff and past guests.