You can tell when there's a couple of letters behind the clock (6)
I believe the answer is:
relate
'you can tell' is the definition.
I can't tell whether this defines the answer.
'there's a couple of letters behind the clock' is the wordplay.
'a couple of letters' can mean two substitutions for 'letter'.
'there's' is a charade indicator (letters next to each other).
'letter' becomes 'r'.
'letter' becomes 'e'.
'behind the clock' becomes 'late' (I've seen this in another clue).
'r' put next to 'e' is 're'.
're'+'late'='RELATE'
'when' is the link.
Can you help me to learn more?
(Other definitions for relate that I've seen before include "Narrate or connect things" , "Tell - marriage counsellors" , "Do well; wave about" , "Recount" , "Sympathise" .)