

alarm-clock-applet
allows custom commands. So put systemctl suspend
into a timer, bingo.
rtcwake
to wake the computer up, for-better-or-worse the music will still be playing.
Someone else mentioned android, VLC there does have a sleep timer (just to stop the music) I didn’t see an equivalent option in the desktop version (at a quick glance) though.
In SMPlayer I do see the option ‘shut down computer’ as a sub-option for `close when finished playback’ (general options)
If would be more productive to encourage blocking by making it more powerful/less of a chore.
Also honestly once a block list is 50+ it already seems like named blocklists are needed to properly manage things.