autofs is the correct solution here. If you have a filesystem listed in /etc/fstab, that means you want it to be mounted at boot. The system tries very hard to achieve that. IF you add the 'bg' mount option then it won't try quite so hard, but it will only reduce that "5 minutes" down to "30 seconds" or similar (I don't recall the details). But for filesystems that don't *have* to be present at boot, use autofs.