Plenty of shows deal with time travel in an episode or two. This is based on trime travel as a way of stopping a very evil man with an improbable name. Vandal Savage. He's not just a Vandal! A man from the future gathers heroes and villains, because of course you'd want that conflict in there. All of the dialogue is corny, and it's a spin-off from 'Green Arrow', so you know it's got to be good.