The Time Travel Car is considered as adjacent to the roof and the inside of the Locomotive. So your Bandit can enter it thanks to a Move action or a Horse action if you play using the Horses and Stagecoach expansion.

Several Bandits can go in the Time Travel Car at the same time, but in order to trigger the action, your Bandit has to be alone in it at the end of a round (after applying the event, if the current round has one).

If this condition is met, all of the other players close their eyes. In the meantime, you must take your Bandit pawn and hide it below the Locomotive;
below one of the Cars; or below the Stagecoach (if you are playing with the expansion). Then, the next Schemin’ phase is played and none of the other players know where your Bandit is. The Bandit’s location is disclosed at the beginning of the Stealin’ phase and the pawn is placed inside the Car where it was hiding. Then all of the actions are resolved.

At the end of the game, after the event is resolved, if one Bandit is alone inside the Time Travel Car, the player receives $500 and all of the loot that may be contained inside.