asciidoc writes timestamps in HTML files it produces.
The date is based in the last modified date of the source file, but is sensible to the timezone.
Prefix asciidoc command with TZ=UTC environment variable (while waiting for 782294)
wait for 782294 . Then use --use-utc-timezone flag with asciidoc.
for manpages generated by a2x through docbook, consider adding ":revdate:" with a manual date (e.g. https://samba.org/~jelmer/socket-wrapper-reproducible.diff)