Coming for a time before Christmas (6)
I believe the answer is:
advent
I believe this clue is a triple definition!
'coming' is the first definition.
(advent is the arrival or coming of something)
'for a time' is the second definition.
(I've seen this before)
'before christmas' is the third definition.
(I've seen this before)
(Other definitions for advent that I've seen before include "Time approaching Christmas" , "Season for a candle?" , "Church season" , "Coming (of Christmas)" , "Second Coming" .)