The reigning Australian GT champion's 2:03.50s best came with 15 of the session's 90 minutes remaining, undercutting Warren Luff's 2:03.79s from earlier this morning.
Mies' entry was already at the top of the order when he joined the circuit thanks to an earlier effort from co-driver Christopher Haase.
Shane van Gisbergen put in a time good enough for second, 0.43s adrift of Mies' ultimate benchmark, before handing over to Jonathon Webb for the closing stages.
Bernd Schneider did the bulk of the running in the car, ending up ninth fastest.
After uninterrupted green running throughout the morning, the third session brought a trio of red flags.
Nick Rowe suffered an early crash at Forrest's Elbow that required a lengthy delay to recover the #94 MARC Mazda from the tyre wall.
A second stoppage ensued when Christer Joens deposited the #9 MPC Audi into the gravel at Hell Corner a short time later, while an issue for the #93 MARC Mazda saw another interruption with just four minutes remaining.
The day's fourth and final practice session is set to get underway at 1545 local time.