The number is 30 days. Roon software requires an internet connection, but supports going offline for up to 30 days. This is a core part of our license checking system. You may not be able to see how this works but the pirates can.
Also, it’s a requirement for lyrics reporting that we must adhere to. Lyrics copyright owners requires monthly reports on lyrics viewed.
EDIT (September 20, 2022):
With the Roon Core on version 2.0, the grace period is not 30 days anymore. You must have internet access to run the Roon Core 2.0. If you require offline access for any substantial period of time, you must stay on 1.8 Legacy.