There is no DRM on GOG. You can just download the offline installer, then install it even without an internet connection. It will never ask you to go online because it doesn't need to check anything.

After digging into it, it seems like the 2 week limit was a bug that has been fixed by steam. So there is no Steam enforced limit, it's up to each game's DRM to enforce restrictions. Steam can function as DRM with a simple command during upload, but it's rather basic and Valve recommends publishers to use additional DRM for more serious protection.

GOG on the other hand is DRM free as a core policy so you're guaranteed no restrictions.