thanks for the reply, but I have a script with interruptions etc. My question was more about how you present them onstage and get the actors to time them with one another.
I'm an actor, and I have done some directing. In my experience, telling actors when to start talking, which words to emphasize, how to time things, etc., are not very fruitful. That is how I would direct myself when I'm trying to convey something, but when I direct someone else, I have to explain why.
Seasoned actors are aware that they are not just saying lines when they hear their cue. They are listening to the other actor. As an actor, it's helpful to understand WHY the lines are overlapping, and why the characters are interrupting each other.
Just some random examples. You could explain it as, "You're just not listening. You want you're turn to talk. You don't even notice that he's still talking." Or, "When he starts talking here, you know what he's going to say, and you don't want to hear it, so you don't let him finish." I don't know what the situation is in the material you are directing, but you get the idea. It usually works better than, "come in right as he's saying this word."
Actors can usually get the rhythm of the scene with notes like these.