The End of Eternity (1976)

Somewhere outside of time as we understand it is the timeless realm known as Eternity, where a group of highly trained technicians – drawn from all the Centuries under their control – have manipulated the Earth’s history to transform it into what they believe to be a perfect world, free from every disaster and hardship. But when Senior Computer Twissel sends a young Technician named Harlan to study the 480th Century in the company of a seductive woman, Harlan begins to suspect that Twissel may have some secret plan of his own which has something to do with the forbidden centuries before time travel was invented...