Add the following mount options:
noauto,x-systemd.automount
The first prevents the early boot process trying to mount the network drive too early, the second creates an on-the-fly systemd automount unit, this is systemd’s equivalent of autofs. The share will be mounted on “first access”, and will not delay the boot process waiting for the server or for the share to mount. Only a program that actually tries to access the not-yet mounted filesystem will be delayed while the share is mounted.
http://www.freedesktop.org/software/systemd/man/systemd.mount.html