Toggling snd_digital_surround used to remove your flash - before the command was removed from the game.  There are/were other commands that remove/d flash but I forgot them.  Also, your DirectX level on game alters the flash time you experience.  Personally, my flash experience has been intermittent.  All I can do is try to turn away from each flash as fast as possible to avoid the lengthy return to normal play.  Sometimes I can see before my sound comes back and sometimes I can hear before my vision comes back.  However, I can always shoot no matter how flashed I am!