Help me identify this sci-fi episode

Many, many years ago I remember seeing a black and white TV show that had the following premis:

A man is seated at a manual typewriter, typing some material. I do not remember the nature of the material, but I have a vague recollection that it was a novel he was working on. The episode spent most of the time observing this activity and I believe he was entirely alone in an office setting. The camera zooms in to the page being typed and we see that the typing starts to slow down, until it essentially stops, mid-word. At this point, the camera begins to withdraw to reveal that the man is actually sitting in a glass cage, in a museum setting, surrounded by galking visitors looking at him, with his hand and a finger poised (apparently) motionless above one of the typewriter's keys. A voice over informs us that the man's metabolism has mysyeriously slowed to the point that the next key will be struck some number of (days/months/years) in the future. This SOUNDS like it would have been a Twilight Zone or Outer Limits episode, but I have been unable to identify or find it. Surely someone can help me in this quest?