When Does "Harbinger" #0 (1992) Take Place?
"Harbinger" #0 v1 "The Beginning" is a superhero comic-book written by David Lapham that released May 1992. So when is "Harbinger" #0 set?
It takes place on the fictional Valiant Universe timeline in the year:
We know this because nearly the entire issue is dated page-by-page.

1991 AD
We know this because nearly the entire issue is dated page-by-page.
Panel 2 on page 1 shows Peter Stanchek writing a letter to the Harbinger Foundation dated "January 30, 1991". Many of the later panels have textboxes with dates from "February 17, 1991" to "May 12, 1991".
It has been retroactively collected into a volume 1 paperback subtitled "Children of the Eighth Day" and a volume 1 hardcover subtitled "The Beginning".
It is among the earliest chronological comic-books in the Valiant Universe (a chronologically first comic to feature the Harbinger characters) and can be read at its timeline point, before "X-O Manowar" #0 (1993) as part of a series of Valiant prologues, or entirely separately.