I have been hoping somebody would bring this back...
Concentrating on bringing the jab back real fast will, ultimately cause you more trouble than it resolves. Things like jabbing on an upward plane and returning the jab on the same line it goes out on will help, as will the positioning of your body; that is, turn your left shoulder and hip towards your opponent. You'll eat fewer left hands than if you are square to your opponent.
But the bottom line is that the right cross is a natural counter to the left jab. If your opponent is looking to hit you with it, he will. And if all you are doing to prevent it is try to retract your jab more rapidly, then he'll hit you easily each time. Because what you are really playing here is a mind game, a game of positioning.
So if you are getting timed with right hands over your jab, invite that counter and counter with your right hand. Hook off the jab. If he is using what you are doing to his advantage, then you are equally free to take what he is doing and use it to yours.