italian_job so to drill down to the particulars you are looking for answers on:
SimpleMobileTools: StorageScope specified folder doesn't reveal music to the app.
Update Frequency: 24 Hours but seems more frequent.
On the first once you have configured storage scopes, you must then add a folder to the playlist either on the main screen or using the 3 dot menu and selected the folder you've granted storage scopes too. Your screen/playlist will then populate with the tracks in the folder.
On the latter if you are feeling that the frequency of the check is more than 24 hours due to the notification that sits there informing you of the system being up to date that should be the case regardless of check frequency between checks unless you've swiped it away and it reappears.
Let me know if this resolves your issue/concern and if not please provide further information to clarify further.