The custom is two men at a time (9)
I believe the answer is:
patronage
'the custom' is the definition.
(I've seen this before)
'two men at a time' is the wordplay.
'two men at' becomes 'patron' (I am not sure about this - if you are sure you should believe this answer much more).
'a time' becomes 'age' (an age is a period of time).
'patron'+'age'='PATRONAGE'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for patronage that I've seen before include "The power to control privileges" , "custom in restaurant?" , "Sponsorship - condescending manner" , "financial backing" , "supporting role" .)