A DC Comics limited-run miniseries, written by Mark Waid, and drawn by numerous artists as a follow up to the incredible (in terms of both art and plot) Kingdom Come.
As a result of the events in Kingdom Come, several cosmic beings from the DC Universe including the wizard Shazam, the god Zeus, the New Gods Highfather, the Guardian of the Universe named Ganthet, and The Phantom Stranger decide to give power to a man who considers himself an apostle of Superman, in the hopes of changing history to better favor this Quintessence of beings, by bringing about a nuclear disaster in Kansas earlier than had happened in Kingdom Come.
However, instead of creating a tool, the Quintessence created a power mad villian who took the name Gog. With unlimited knowledge of and power to manipulate multiple timelines, Gog begins murdering Superman repeatedly ... each murder taking place a day earlier than the prior one.
This paradox puts an incredible strain on the "true" timeline that the superheroes think is the only timeline that exists. As a result, the Superman, Wonder Woman and Batman of the Kingdom Come timeline, with the aid of the Linear Man Rip Hunter decide to travel back to the past in order to stop Gog from murdering more Supermen.
This decision in and of itself seems to ensure that the events presented in Kingdom Come will never come to pass, causing several heroes of that time, including Ibn Al Xu'Ffasch (son of Bruce Wayne, grandson of Ra's Al Ghul), Nightstar (aka Mar'i, daughter of Nightwing (aka Dick Grayson) and Starfire), Offspring (son of Plastic Man) and Kid Flash (daughter of The Flash (aka Wally West)) to try to stop the erasure of their timeline, and existence.
In a final confrontation in the restaurant run by Booster Gold called Planet Krypton, Gog and the heroes from the various timelines learn of the existence of hypertime, revealed to them by Jonathan, the son of the Kingdom Come Superman and Wonder Woman ... Jonathan may also be the true identity of The Phantom Stranger, though this is never implicitly stated in the books.
The end result of the series solves many of the continuity problems brought about by more than 65 years of DC Comics history, as well explaining the apparent inconsistencies raised by both Crisis on Infinite Earths and Zero Hour.
As explained by Rip Hunter:
"Off the central timeline ... exist divergent "tributaries" ... an infinite realm of parallel worlds and timelines where reality as you know it has taken different twists and turns...
But what's astounding is there's far more to it than that. On occasion, those tributaries return -- sometimes feeding back into the central timeline, other times overlapping it briefly before charting an entirely new course...
An old friend is suddenly recalled after years of being forgotten. A scrap of history becomes misremembered, even reinvented in the common wisdom. It is a kingdom of wonder."
While some DC Comics readers feared that hypertime would be used to explain such mundane things as inking errors, it hasn't actually turned out that way. Much of the promise of the hypertime concept has yet to be explored.