Tales of time traveling don't always have the firmest rules but there are some generic "truths" being said by the experts. Stories are known as the Butterfly effect where time travelers explain that they cannot change the past without shifting the future. It is a concept of creating a paradox, such as by meeting your past or future self. While these "law" explains results of time travel, they are generally adopted in sci-fi movies and TV series.
On "Legends of Tomorrow," the same rules apply but only a little vaguer. Several characters have mingled with their past selves, none more than Martin Stein who had multiple conversations with his younger self. As for altering the timeline, they'll sometimes let the small things intact.
The Synopsis Season Finale
"Aruba - As the Legends are about to liftoff for their next destination, a massive time-quake rocks the ship. To try and fix what has happened, they are forced to break the one basic rule of time travel. But if they can destroy the spear, they will face the ultimate aftermath. Victor Garber, Brandon Routh, Arthur Darvill, Caity Lotz, Dominic Purcell, Franz Drameh, Nick Zano and Maisie Richardson-Sellers. Rob Seidenglanz directed the episode. Phil Klemmer & Marc Guggenheim wrote the script. Original airdate 4/4/2017."
Legends Are Going To Break The Rules Of Time Traveling
Executive producer Marc Guggenheim exposed some of the character's appearance in the finale including The Legion of Doom, Captain Cold, Laurel Lance, and J.R.R. Tolkien. Since the promotion and synopsis for the upcoming episode "Fellowship of the Spear" consist of Captain Cold and Tolkien, it seems likely that "Aruba" is going to be profoundly set up there.
Before completing "Aruba", however, the Legends will have to deal with "Doomworld" when the Legion of Doom changes reality with the spear. Whether the implications from that are also disturbing the events in "Aruba" remains to be seen. Legends will also be forced to face the outcome of the choices they make to destroy the spear and save reality.
"Legends of Tomorrow" airs Tuesday, March 21 at 9 pm on The CW.