Mark clock setting (4)
I believe the answer is:
spot
This clue is a triple definition!
'mark' is the first definition.
(I know that spot is a type of mark)
'clock' is the second definition.
(clock can mean to notice or spot)
'setting' is the third definition.
(thesaurus)
(Other definitions for spot that I've seen before include "moral flaw" , "Blob" , "jam > stain" , "Predicament" , "Notice - place" .)