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 anagramming the letters (I've seen this in other clues).
'at' says to put letters next to each other.
'central' indicates the central letters.
The centre of 'greenwich' is 'n'.
'on'+'time'='ontime'
'ontime' with letters rearranged 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" .)