What makes telly so awful about the first of December, according to the Julian calendar (3,5)

I believe the answer is:

old style

I'm a little stuck... Click here to teach me more about this clue!

'julian calendar' is the definition.
(synonyms)

I don't understand the remainder of the clue.

(Other definitions for old style that I've seen before include "Traditional, retro" , "Traditional type" , "how Julius arranged his dates" .)

Want a hint initially instead of a full solution? Install my app