Tander was almost a second clear of the field in the first of two half-hour sessions when he drove the #777 The Bend Audi R8 LMS Evo to a 2:04.9848s.
Yasser Shahin ended up second in Practice 2 and had started Practice 1 in the #777 Audi before Tander took over.
The four-time Bathurst 1000 winner took two laps to improve on Shahin's 2:08.4424s at that point, but when he did, he moved from third to first with a 2:05.6898s.
Tander set the very fastest lap of the day next time around, while Stephen Grove improved marginally with the chequered flag out to consolidate second spot for the #4 Grove Racing Porsche 911 GT3 R on a 2:05.8074s.
Van Gisbergen subsequently moved to third with a 2:06.3123s in the #888 Triple Eight Race Engineering Mercedes-AMG GT3, a lap which no one would beat in the following session.
Wall/Adrian Deitz are therefore fourth-fastest on combined session times, ahead of Trophy Series competitor Brett Hobson, who drove the #96 Nissan Nismo GT-R to a 2:07.5435s in Practice 1.
Mostert's best of a 2:08.4675s in his brief run at the start of Practice 2 leaves the #24 Bostik Audi R8 LMS Evo, which he shares with Tony Bates, sixth on the timesheet after the two sessions.
The latter of those ended just over five minutes early due to a late red flag, after Trophy driver Brad Schumacher (#55 Audi R8 LMS Ultra) blew a tyre and spun into the wall on Conrod Straight.
Both qualifying sessions, which set the starting grid for Race 1 of the weekend, take place tomorrow from 09:05 local time/AEDT.
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