United go over stopping time to attack — it’s not going to work (5,3)

'not going to work' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'united go over stopping time to attack' is the wordplay.
'united' becomes 'U' (abbreviation as in Man U for Manchester United).
'go over' becomes 'vet' (vetting is a kind of going over).
'stopping' indicates putting letters inside (stopping can mean blocking a gap).
'time to attack' becomes 'd-day' (I've seen this in another clue).
'u'+'vet'='uvet'
'uvet' inserted into 'dday' is 'DUVET DAY'.

'it's' acts as a link.

Can you help me to learn more?