Originally Posted by
Dataweaver
For the sliding timeline, you could do worse than to take the timeline from Zero Hour #0 and add six years to it. Starting with:
35 (now 41) years ago: J'onn J'onzz accidentally teleported to Earth
33 (now 39) years ago: Kal-El arrived on Earth, landing near Smallville
30 (now 36) years ago: Captain Comet
25 (now 31) years ago: Bruce Wayne's parent killed; Project Atom begins.
15 (now 21) years ago: Clark Kent leaves Smallville for Metropolis; Cave Carson; Sea Devils; Sarge Steel; Doom Patrol; Animal Man; Alec Holland becomes Swamp Thing.
13 (now 19) years ago: Metal Men; Metamorpho; Challengers of the Unknown; Deadman.
11 (now 17) years ago: Oliver Queen stranded in a desert island, learns archery.
10 (now 16) years ago: the new heroic age begins. Superman, Batman, the Joker, Catwoman, Flash, Green Lantern, Martian Manhunter, Black Canary, Aquaman, Adam Strange, Katar Hol, JLA.
9 (now 15) years ago: the Atom, Elongated Man; Doom Patrol dies; Creeper; Hawk and Dove; New Gods; Zatanna.
8 (now 14) years ago: Dick Grayson becomes Robin.
7 (now 13) years ago: Teen Titans form.
6 (now 12) years ago: Rose and Thorn; Black Lightning.
5 (now 11) years ago: Ted Kord becomes Blue Beetle; Captain Atom arrives in present; Firestorm. New Teen Titans form.
4 (now 10) years ago: Outsiders form. Crisis on Infinite Earths. Captain Marvel. The Question. Vigilante.
3 (now 9) years ago: JLI. Killing Joke, Death in the Family. Outsiders disband.
2 (now 8) years ago: LEGION, Starman (Will Payton).
1 (now 7) year ago: Tim Drake becomes Robin. JSA returns from Ragnarok.
0 (now 6) years ago: Death of Superman; Knightfall; Emerald Twilight; Zero Hour.
Some details need to be adjusted: e.g., ZH#0 has Wonder Woman arriving just after the Crisis on Infinite Earths. And, of course, it would need to be extended to cover the next six years as well: Morrison's JLA, Young Justice, the Titans and JSA revivals; Infinite Crisis; Final Crisis; Flashpoint; Rebirth; Dark Nights; etc. But this could be viewed as a rough outline for the sliding timeline.
It's still a bit too condensed for my liking; I'd personally prefer another four years on the front end, giving ten years from Superman's debut to the Crisis on Infinite Earths. But that's a heck of a lot better than the timeline being three years shorter.
Another possibility would be to assume roughly a 4:1 time ratio: 1957–1969 are covered by the first three years; 1969–1985 would be another four years; 1985–1995 would be two and a half years; 1995–2005 would be another two and a half; 2005–2011 would be 1˝ years; 2011–2015 would be one year; and 2015–2023 would be two years. Total time from start to finish: 16˝ years. And when we hit 2038 (the 100th anniversary of Superman's debut), we'd be up to a 20-year sliding timeline.
A 3:1 ratio might work better, though: four years from 1958 to 1970; five years from 1970 to 1985; three years from 1985 to 1994; four years from 1994 to 2006; two years from 2006 to 2012; one year from 2012 to 2015; and two years from 2015 to 2021. Twenty-one years total.