Nope--There was an episode where the Enterprise went back in time and captured an Air Force pilot. He had seen them flying above his plane. He couldn't be returned to Earth because to do so would have changed the future. They went down to his airbase to get back the films his plane's cameras had taken and were captured themselves by the M.P.'s. Eventually, they determined that he had to be returned to Earth because his son...who hadn't yet been born...would eventually lead and expedition to Saturn. So they flew towards the sun and flew a bi further back in time, used the slingshot effect to head back towards their time. Along the way, they returned him to his jet, in flight, just before he had seen them. All through that last sequence, the digital clock ran first backwards and then forwards. It was season 1, episode 19. "Tomorrow is Yesterday."