Yes, the updates for Linux are delayed because they are uploaded not by us but by the GOG team.
We appreciate the thing you've made, but seeing this issue with delays.... [...]
Please allow me to share information that your wording suggests that you're missing.
A Win or MacOS user on GOG can install their games in one of two ways - using GOG's client (GOG Galaxy), or standalone installers they download via the site. There is no client for Linux users, so they're limited to the latter way.
Devs/pubs push updates via the dev portal, and said updates are made immediately available to those using the client.
Updates for standalone installers are tested and packaged by GOG before being made available for download as standalone executables.
Changelogs are not available on the client, they are only added to one's library on the site.
Changelogs are usually made available along with the updates of standalone installers.
To sum things up - you uploaded the update on Mar 2 via the dev portal, and those using the client got it on that day, while those not using the client got the update in their library on Mar 5, along with the changelog.