Entering through the rear doors (the main doors are still locked at that time) she climbs to her second-floor office.
After finishing some preparation work, she walks down to the first floor, and into the On-Air Studio. She flicks on the lights, illuminating the entire two-room studio.
Well, that was then. Now she switches on only one light; she's doing it to help save the planet.
"There aren't a lot of people in the building [that early], so I feel scared," 28-year-old Au says as she shows me the thick glass partition separating the studio.
"Before when I entered, I'd turn on both lights - the room outside and inside - but I actually didn't use the room inside. I felt scared so I turned on the lights."
Au's change of habit is part of her efforts to reduce electricity consumption.
She and two other colleagues - DJs Donald Tong Kin-hong and Danny So Yiu-chung - are involved in the My 10 Days programme, an initiative run by the global conservation body WWF, to promote a greener lifestyle in conjunction with Earth Hour 2012.
"WWF asked us about our habits in using electricity," said Au on day five of her 10 Days programme. "We had to think about how we waste electricity and ways to reduce our usage. Then we came up with our 'aims'."
The aims she speaks of are the three goals that each of the DJs committed to as part of their individual 10 Days programme.
Using only one light in the studio is one of Au's aims. Another involves limiting her hair-drying time to less than four minutes (she used to spend 8 to 10 minutes). Her last aim, which has been the most difficult, yet most physically rewarding, involves cycling once a week to the Chinese University of Hong Kong, where she's pursuing post-graduate studies in fine arts.
These may not seem like Earth-shattering sacrifices. Nor were they designed to be. Small contributions make a difference. We don't need to completely change our way of life in order to contribute. That's not sustainable.
Au is determined to continue her energy-saving lifestyle.
"My tasks have kind of become a habit for me," she says on the last day of her 10 Days. "I'm used to turning off the lights and drying my hair in under four minutes now. I'll continue. Actually, it's not difficult."
Her cycling aim will have to be modified. She does not go home directly after class sometimes, so it's impractical to use her bike. She'll switch to riding her bike to her art studio now. It means that she can leave it there if she has to go out later.
As the 60+ logo for Earth Hour suggests, we must go beyond one hour and consume less - each and every day. Set your own energy-saving targets. With the global community involved, every sacrifice makes a big difference.
The global Earth Hour is tomorrow from 8.30pm to 9.30pm. WWF calls on supporters to turn off all non-essential electrical equipment