Alice Sheldon's "The Man Who Walked Home" (as by James Tiptree, Jr) (short story, post apocalypse, free)
Story summary.At the site of the time travel experiment, there was an explosion, a crater, & the side effects that killed much life of earth. But there is also a curious physical phenomenon that is a side effect of original experiment: once a day, every year, at the same time, at a place in the original crater, a "monster" appears for a few seconds - a monster that appears to be moving but is not, it leaves bad smell after it's gone, & any attempt to touch it tends to cost you your limbs.
Story is mostly a view of this curious phenomenon, & eventually an explanation, from the point of view of sundry people who'll watch it over the centuries as the dead place keeps slowly getting inhabited.
Fact sheet.First published: Amazing Science Fiction, November 1972.
Download full text from Baen eBooks.
Related: Stories of Alice Sheldon (as by James Tiptree, Jr).