It may be on time at central Greenwich, say (7)
I believe the answer is:
mention
'say' is the definition.
(mentioning is a kind of saying)
'it may be on time at central greenwich' is the wordplay.
'it may be' indicates an anagram (I've seen this in other clues).
'at' says to put letters next to each other.
'central' means to look at the middle letters.
The middle letter of 'greenwich' is 'n'.
'on'+'time'='ontime'
'ontime' anagrammed gives 'mentio'.
'mentio'+'n'='MENTION'
(Other definitions for mention that I've seen before include "Briefly refer to (something)" , "Cite; quote" , "Make reference to" , "state" , "Speak of - refer to" .)