There should be a video of this feature somewhere on the EA website. You can throw a pass to the receiver as soon as he makes his break. What it comes down to is you can't throw the ball to a receiver until he is realistically prepared to catch it.
Think of it this way: if you're running a 12 yard square out on 3rd and 10, you aren't going to be looking for the ball during your 12 yard stem. Only after you break to the sideline will you turn your head looking for the ball. So in the game, only after WR# 80 has broken to the sideline will his icon light up, enabling the QB to throw the pass.
This has nothing to do with coverage though. If he is absolutely blanketed by 3 DBs, but has made his break and is expecting the ball, you can still fire it right at a corner's chest.