You don't need a timer and I would not want to see one in game.
This is a realism mod, so just use it like you would in real life. Aim, wait a second, exhale slowly, then fire.
I enjoy the fact that there is no visual cue telling me when to fire. It is up to me to develop a sense of when my aim has settled. Even with machine gun fire exploding around me, I have to force myself to wait, breath, then fire when I feel it is ready. Much more fun than just staring at a stupid counter.