it varies from person to person. A large delay typically results in a larger effect for people who don't stutter. For people who do stutter there's a fine tuning that goes on to find the "optimal" delay. For most people it ranges from 50-250 ms (250 is really quiet long). If you listen to one of Link's calls (I think the second, not sure though) you can hear the delay just after he takes his headset off. It was a long delay. A very long delay, more than 250ms I would suspect.