Some couples do this over start of holiday in Cuba? Not a huge amount (7)
I believe the answer is:
cohabit
'some couples do this' is the definition.
The definition suggests a singular noun but the answer is not.
'start of holiday in cuba? not a huge amount' is the wordplay.
'start' indicates taking the first letters.
'in' indicates putting letters inside.
'cuba?' becomes 'c'.
'not a huge amount' becomes 'abit' (I am not sure about this - if you are sure you should believe this answer much more).
The initial letters of 'of holiday' is 'oh'.
'c'+'abit'='cabit'
'oh' inserted within 'cabit' is 'COHABIT'.
'over' acts as a link.
Can you help me to learn more?
(Other definitions for cohabit that I've seen before include "Live together as husband and wife" , "shack up" , "House-share" , "16 ac 17 ac" , "What some items do" .)