.ark files, what do they contain

[123]

In my saved folder there's several files called Ragnarok_03_04_2019_<time>.ark , are they snapshot files and how are they unpacked?

[Ancient]

The timestamped ones are just older backups of the world save. Your current active save that the server will actually load will be named Ragnarok.ark.

[Panda]

As Ancient said, the timestamped ones are backups of your current save (Ragnarok.ark). You can revert to the backup save at any point by renaming one of the timestamped files to just 'Ragnarok.ark[\b]. Make sure you keep the original Ragnarok.ark file though in case you need to go back to it if something is wrong with your backup save(s).

[Toooni]

Thats what you're searching for:
https://github.com/Qowyn/ark-tools/releases