Second vehicle's first in concrete discharge (7)
I believe the answer is:
removal
'discharge' is the definition.
(removal is a kind of discharge)
'second vehicle's first in concrete' is the wordplay.
'second' becomes 'mo' (both are short periods of time**).
'first' indicates taking the first letters.
'in' is an insertion indicator.
'concrete' becomes 'real' ('real' can be similar in meaning to 'concrete').
The first letter of 'vehicle' is 'v'.
'mo'+'v'='mov'
'mov' inserted inside 'real' is 'REMOVAL'.
(Other definitions for removal that I've seen before include "Sack" , "Taking (of thing) away" , "Transference" , "Ejection" , "These vans dispatch your house contents" .)