...
.... The drive is normally only used at 3am to run a backup script, ...
When I mount the drive manually, the timeout always succeeds (though again after 300 seconds rather than 120).
Any ideas?
not for btrfs-automount-case. but you {s,c]ould check with your script if the drive is mounted *before* backup starts. And I would check if the mount point is still clean (in case the backup blindy backuped to the mount point without mounted drive)