Perhaps UniversalExtractor could work extracting the files from the installer without altering the datestamp of the files, that's a long shot by a very very far way.

gerwin: try innounp or innoextract.

Srandista, you were right it is an InnoSetup v5.6.2 installer.
innoextract does not know this version.
Innounp v4.9 can extract it to some degree. But the compressed files are still there in compressed form, with their CRC or something as filename and with the date of packing.

Example used:
setup_rise_of_the_triad_1.3_(28045).exe, packed 22-03-2019, changed+changes all file dates.
Not all packages are affected (yet), like:
setup_star_control_2.1.0.13.exe, packed 19-01-2015, retains original file dates.

To be fair, the lost timestamps in many of these cases are the timestamps of when their intern (either GOG's or the publisher's) installed whatever copy they found through DOSBox 0.70 and packed them up since. They're no better than warez sites 'preserving' torrentzip copies from warez sites.

Yeah I know a bit about GOG's way of working. Though, software with erased timestamps is very bad practice in my opinion, even for them. Time stamps are one of the few leads in version control, I use it often. Now GOG erases it when packing it up, and it gets erased again when installing.
Question is, are they gonna do this with all their software now? Are they even aware that they are doing this?