Another idea might be a solution from a stable release thread
Possible 2 Min delay on shutdown with Gnome
If you got the problem with shutdown delay (about 2min) on Gnome, here is a workaround:
Edit /usr/lib/systemd/user/gnome-session-restart-dbus.service in your favourite editor as root and add Slice=-.slice as a line all by itself like this:
[Service]
Type=notify
Slice=-.slice
ExecStart=/usr/lib/gnome-session-ctl --restart-dbus
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