I would imagine that would depend upon your regional union contract, but I could be wrong. Hopefully others will come along that know more than I do.
That's pretty much everyone here.
12 months for family coverage is for part time employees (or at least most of them-there are some exceptions).
For full time driver (permanent, not seasonal or casual), everything I've ever seen was full coverage (family) shortly after completing the probationary period. So roughly 2-4 months after starting.