Army taking time to get one desiring release (7)
I believe the answer is:
hostage
'one desiring release' is the definition.
(hostages are held against their will)
'army taking time' is the wordplay.
'army' becomes 'host' (host is a kind of army).
'taking' is a charade indicator (letters next to each other).
'time' becomes 'age' (an age is a period of time).
'host'+'age'='HOSTAGE'
'to get' acts as a link.
(Other definitions for hostage that I've seen before include "Prisoner - pawn" , "One held for ransom" , "One held captive" , "Detainee - gash toe (anag)" , "Captive held for ransom" .)