ACMA is the regulator, but I wasn't able to find anything on their website about broadcasters having to adhere strictly to their published timetables when I looked a few weeks ago.
Even if they did, any discrepancy between the PVR's clock and the broadcaster's clock will mean that you're likely to lose a bit of the start or end of any program if you don't use some padding, simply because there is typically no "filler" between the titles of one program and the start of the next.