At least in the UK and I would assume that other ISP's worldwide may also do the same, employ broadband bandwidth caps/restrictions. Most (good) ISP's also include certain time periods when no cap exists.
I'd like to suggest a Spotify configuration option that allows me to restrict the synchronisation/downloading of Offline Content to certain periods.
The default operating behaviour could be set to no restriction so as not effect existing users.
If 'restricted access' is selected by the user, two further fields consisting of a start and end time would be used to only allow Spotify to perform synchronisation or downloading of Offline material during those times.
As an example:
my UK based ISP allows me unmetered bandwidth between 12am and 8am.
I would set Spotify to only allow synchronisation between 12.30am and 7.30am.
Any bandwidth used by Spotify would no longer count towards my monthly bandwidth cap set by my ISP.
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