Comment # 21 on bug 909912 from Olaf Hering

(In reply to Olaf Hering from comment #20)

>   x-systemd.device-timeout=12

This option has to go into fstab.

I think what happens is that one branch processes crypttab and another fstab.
There is no connection between both. Even if the timeout paramemter for
crypttab would be processed, the other branch for fstab waits for the entry to
appear. Since it has no idea what the backing device is it times out. 

Both seem to lack the concept of "wait forever".

So the workaround is to append "x-systemd.device-timeout=1234567890h" to all
the mount options in fstab for devices backed by crypttab entries.