The build timestamp is embedded in various .dvi files:

https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/diffoscope-results/chktex.html

  /usr/share/doc/chktex/ChkTeX.dvi.gz

  ··TeX·output·2021.
vs.
  ··TeX·output·2022.

  ··08.23:1518
vs.
  ··09.26:2344..

The attached patch fixes this by setting FORCE_SOURCE_DATE=1 in
debian/rules, which texlive needs in order to respect SOURCE_DATE_EPOCH,
which is set during debian package builds to the timestamp in the latest
debian/changelog entry.

https://reproducible-builds.org/docs/source-date-epoch/

It also removes what appears to be some code attempting to adjust the
timestamsp in the tex.in files, which was only partially effective, and
is no longer needed.

With this patch applied, chktex should build reproducibly on
tests.reproducible-builds.org

Thanks for maintaining chktex!

live well,
  vagrant

We believe that the bug you reported is fixed in the latest version of
chktex, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 995650@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Thorsten Alteholz <debian@alteholz.de> (supplier of updated chktex package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Sun, 19 Jun 2022 22:40:03 +0200
Source: chktex
Architecture: source
Version: 1.7.6-5
Distribution: unstable
Urgency: medium
Maintainer: Thorsten Alteholz <debian@alteholz.de>
Changed-By: Thorsten Alteholz <debian@alteholz.de>
Closes: 995650 1000070
Changes:
 chktex (1.7.6-5) unstable; urgency=medium
 .
   * depend on PCRE2 instead of PCRE3 (Closes: #1000070)
   * debian/control: bump standard to 4.6.1 (no changes)
   * debian/control: use dh13
   * debian/control: add Rules-Requires-Root: no
   * debian/rules: move to dh
   * debian/rules: make it reproducible (Closes: #995650)
                   Thanks to Vagrant Cascadian for the patch
Checksums-Sha1:
 24bc6593d9d40433435ce21b6766ea62b8df4fb3 2064 chktex_1.7.6-5.dsc
 08316be4888af58e285a4a933114cd6fd0c29968 44576 chktex_1.7.6-5.debian.tar.xz
 0ab9bc2fed02c1a72dc8670951d70c27a18167be 9698 chktex_1.7.6-5_amd64.buildinfo
Checksums-Sha256:
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Files:
 a39220cd5df5e539f8f9630ce08c4408 2064 tex optional chktex_1.7.6-5.dsc
 da2d39515586b21de94adbc244aa7773 44576 tex optional chktex_1.7.6-5.debian.tar.xz
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