It is first necessary to establish what, precisely, is being asked by that question, since most casual answers are actually responding to the perceived question ‘how is time measured,’ and not to the actual question ‘what is time’.
All of an Instant Review
Alternative world (or secondary world) fantasy gets all the attention these days as the quintessential owner of the steepest learning curves, but those expositionary slopes are molehills compared to the mountainous terrain to be conquered in the hardest of science fiction that the genre has to offer, like Garfinkle's All of an Instant.
Effect and Cause
A recent Writing Excuses episode to which I listened discussed the ideas of disordered storytelling, and means of writing stories that are intended to be read in an order other than from the first page to the last page. Unfortunately, it didn't really dig into the topic the way I hoped it would engage with it.
The Variable Man Review
The Variable Man’s description included references to a post-nuclear apocalypse Earth, and a man from the past. Whatever I expected from that sparse summary, it was not what the story proved to be. The fact that the Earth set piece happened to have undergone a nuclear apocalypse (at least five of them, actually) is really something of a footnote, one of those throw-away world-building tidbits, like villius flowers, that don’t really add to the plot or the substance of the story, and exist only to create a more full-fleshed world. As for the man from the past…that’s where things got interesting.
IGC Publishing 