Lost in Space Season 3 Episode 18

The Time Merchant

Will is conducting an experiment in a cave and captures a man who claims to be the man who controls time for the entire universe. This ""Time Merchant"" takes Will, Professor Robinson, Smith, and the Robot, to his secret lair. From there, Smith uses the Time Merchant's time machine to return himself to Earth on the day the Robinson's departed, with the objective of NOT sabotaging the Jupiter II mission and letting the Robinsons go on their way to Alpha Centauri. The Time Merchant then announces that if Smith does not get on the Jupiter II, the ship will not fly off course and will therefore be destroyed by a collision with an asteroid several months after liftoff. So Will is sent back to join Smith and try to convince him to get on the Jupiter II as he originally did.