You will need to contact a local electrician to:
1. Move your hot water circuit from the off peak terminal to the standard tariff terminal on your meter.
2. Put a timer on the hot water circuit to only run during the day or use a hot water diverter like this one https://www.catchpower.com.au/.
3. Put a work request to the local electricity distributor to remove the off peak tariff programming internally in the meter. (Electricity retailer might also do this - Depends on your state)
However most of the time, this is a false sense of economy as the off peak tariff is usually around the price you get for solar export. So you will spend $400-$800 installing timers/hot water diverters to save 2c or 3c per kWh. (That's a long payback)
I would like to heat our water during the day to take advantage of our solar. How do I turn off the “off peak” feature? myindigocard
If you are leaving the house empty for more than a few days, it should be safe to leave your heating on, however, even if you do turn off the water. It can be useful to have your central heating ticking over on a low temperature while you're not there with the help of a smart thermostat.