I don't think the over-travel affects the CURRENT bullet being fired. A 1000 FPS bullet is already a foot away from the breech in 1/1000 of a second. If you had a 6" barrel, that would mean that the bullet exits the muzzle in 1/2000 of a second. I doubt that your finger does anything after the trigger break within 1/2000 of a second that would disturb the current bullet in flight.
It certainly might disturb the ability to follow up on the next shot if that finger movement was excessive and caused you to move off target more than a finger that stopped a very short distance behind the break point.