The Twilight Zone - Ninety Years Without Slumbering

Sam Forstman is an old man who lives with his granddaughter Marnie Kirk and her husband Doug. Sam lives a simple life and doesn't sleep much anymore. He's usually up at all hours tinkering on his grandfather clock, something that worries Marnie as his attention to the timepiece verges on the obsessive. The reason for that however is quite simple: he is convinced that should the clock ever stop, he will die.