The 161-lap race was set to start at 11:30 local time/AEDT but will instead start at 11:00 local time.
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The Bureau of Meteorology has forecast showers and a chance of thunderstorms in the morning and afternoon on Sunday.
Speedcafe.com understands Supercars began discussing bringing the race start forward on Thursday afternoon.
A forecast issued on Thursday morning predicted a 100 percent chance of rain between 15mm to 20mm.
However, a second forecast issued at 16:30 local time/AEDT has since been revised to an 80 percent chance and up to 10mm of rain.
Last year's Bathurst 1000 was hit by rain in practice, but Sunday's race was a dry affair throughout.
That year's race started at 11:10 local time, with lights out at 11:15, and ran for a little over seven hours.