To avoid hanging out the system while mounting NFS shares on boot time add the option bg to the /etc/fstab, example: /plex/4T        nfs     rw,bg      0       0

This will help to boot and in background continue trying to mount in case of getting a "time out"

From the man page: mount_nfs

bg      If an initial attempt to contact the server fails, fork
        off a child to keep trying the mount in the background.
        Useful for fstab(5), where the file system mount is not
        critical to multiuser operation.