I couldn't find much info about this online so I decided to write up my experiences with it, in case someone next year has the unfortunate circumstance of requiring this.
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It was exactly two weeks after the date of the regular UMAT, and was held in ACER's main building, in Camberwell. There were about 15-20 other people there, so it was relatively relaxed. If you arrive early, they give you a seat in their atrium area until the time written on your admission ticket. This was 9.00 AM this year.
Once going upstairs, we had to sign in. Since there were so few people, this was a relatively painless process. After signing in, we sat inside the testing room, waiting until 9.30 for the remaining two people to arrive. The Tables were quite large, and the chairs were cushioned and designed for comfort which was nice.
The nice ladies offered us glasses of water, but from then on testing procedures commenced and I'd imagine it was like the regular UMAT test. I believe the exam papers had the same questions as those of the previous sessions.
I hope someone finds this useful in the future
If you have any other questions ask.