Watches showing end of time? Certainly! (4)
I believe the answer is:
eyes
'watches' is the definition.
(to eye is to watch or look at)
'end of time? certainly' is the wordplay.
'end of' indicates one should take the final letters.
'certainly' becomes 'yes' (both can be used to answer in the affirmative).
The last letter of 'time' is 'e'.
'e'+'yes'='EYES'
'showing' is the link.
(Other definitions for eyes that I've seen before include "They see and" , "Are they made to suggest possible date" , "Visual organs" , "Closely looks at" , "Peacock's tail markings" .)