I just got an answer back from the case officer. Here's what he says:
Temporary visas
Clauses 173.511 and 884.511 provide that, if the applicant is not a CPNC, a temporary visa will be granted permitting the holder to travel to, enter and remain in Australia for 2 years from a date specified by the Minister for that purpose.
For a subclass 173 visa holder, the temporary visa is in effect for a period of 2 years from the date of initial entry into Australia. This means that the visa will allow the subclass 173 holder to remain lawfully in Australia for 2 years from the date of initial entry to Australia. However, the travel facility may only allow the holder to leave and “re-enter” Australia for 2 years from the date of visa grant.
For a subclass 884 visa holder, the temporary visa is in effect for a period of 2 years form the date of visa grant.
looks like it's from the date of entry.