Greek character taking time to make special mark (6)
I believe the answer is:
stigma
'special mark' is the definition.
(marks of crucifixion left on Jesus Christ's body)
'greek character taking time' is the wordplay.
'greek character' becomes 'sigma' (letter from the Greek alphabet).
'taking' is an insertion indicator.
'time' becomes 't'.
'sigma' enclosing 't' is 'STIGMA'.
'to make' acts as a link.
(Other definitions for stigma that I've seen before include "Sign of disgrace" , "A stain as on character" , "Symbol of disgrace or infamy" , "Mark of shame, stain on reputation" , "Part of a flower" .)