Our controlled load was available for the HWS from 2330 - 0630 each day here in SA, 8 hours.
I think all states and possibly regional power suppliers have different times, tariffs, supply charges etc, so maybe the statement on the AGL site is a blanket type overview.
We are off CL now, was too confusing on TOU smart meter data, now it's simple, we time the HWS for cheapest use, and even during solar soak if clear days are going to allow for the 3.6kw use over the 30 - 45 mins once a day that it's heating.
I'm not aware a consumer has the ability to ask for special timings, I would think highly unlikely.
Not sure if it would be retailer (AGL) or the supplier that sets that.