Do they create alternate timelines when they change things in the past?Quantum Mechanics says that any decision we make exists,we only get to experience to effects of ONE of those decisions.So in another timeline we made the opposite decision.So every time the Legends change something in the past,they create an alternate timeline.

And of course going by THAT logic,that means there's a timeline in which Laurel Lance was never killed.Of course that timeline would be the original DC Comics timeline,meaning the Legends now exist in an alternate timeline.