What did "Teaching of the Twelve Apostles" say about the Epiphany?

I was reading the "Teaching of the Twelve Apostles" to answer another question on this site and chanced upon a strange tidbit that I don't understand the meaning of: > The apostles further appointed: Celebrate the day of the Epiphany of our Saviour, which is the chief of the festivals of the Church, on the sixth day of the latter Canun, in the long number of the Greeks. > > ["Teaching of the Twelve Apostles"](http://www.newadvent.org/fathers/0854.htm) What I'd like to know is: - What day of the year was that? - Was this the same Epiphany we know today (i.e., January 6th or thereabouts)? - Why was this the "chief of the festivals?" (What about Easter and Pentecost?)