Hypertext Time is the metafictional pseudoscientific theory that time is like a web page. History resembles a vast mosaic of discrete events, much like web pages, joined by metaphorical hypertext links that connect one moment to the next. When time travel or retcons change these events, the "links" may not be updated immediately or at all, resulting in temporal anomalies. Paradoxically, this increases the stability of the timeline, allowing structurally-important events to stay in place even as everything changes around them. Furthermore, the previous versions of history still exist, and may be "restored from backup" via temporal change or Writer fiat.
Like all ridiculous theories in comics, it's absolutely true, and the term "Hypertext Time" also refers to the layers of superseded history that result from this. Higher-dimensional beings, like Mister Morrison and Chaos Theory, have the ability to navigate this possibility space.
(It's also a blatant parody of DC Comics's Hypertime, but shhhh. It's not like they're using it.)
One of the most infamous cruxes of Hypertext Time is who or what killed the dinosaurs. This has been attributed to the planet Net.mesis, the RACelestials, and Flatulence Lad. Because of the nature of Hypertext Time, all these versions are true.