Is it possible to win a level after the countdown from firing your gun is over?
As far as I can tell, you have only one option:
Shoot the police officer standing at the subway entrance.
To do this you have to be standing somewhere where he cannot see you - so you don't get shot first - so firing from somewhere inside and dark, such as a darkened window or doorway will work.
It wouldn't surprise me if this wasn't possible on all levels.