Apple Tree Wassailing to my knowledge is carried out on "OLD Twelth Night" which is January 17th, at least in the Tradition we base ours around. Unfortunately that means around -20 degC on a lot of the Canadian nights we have done it.
We base ours on the Carhampton version and sing their song, amongst others if it's only around -5C. We also Morris Dance and do the cider soaked toast thing. We also had a real musket once.
Our other tradition is to soak a fruit cake in Brandy and NOT manage to light it because it's too damned cold. Last year this un-broken tradition died out in a small blue flame, it was only a couple of degrees below Zero. Such is Tradition.
Loads of Wassailing info HERE
JohnB