Play was due to start at 11:00am (0000 GMT) but persistent drizzle meant there was no action until 5:00pm, when matches resumed.
It followed intense heat and then torrential rain playing havoc on Tuesday, with hours of delays and a slew of matches held up.
Those delayed matches were due to get under way early Wednesday, with the doubles competition also scheduled to start.
But only matches on the three main stadiums, which have roofs, were able to begin on time.
Briton Jamie Murray, a top doubles player and brother of Andy Murray, hit out at Wednesday's schedule being released so late on Tuesday evening that some players went to sleep not knowing when they would start.
"11 am start on outside courts. Players arrive approx 8-830am," he said on Twitter. "Schedule released 1130pm. Unfair.
"On top of that the weather is crap. Just start matches later and give players more rest/prep time. You have lights!"
Belgian veteran Kirsten Flipkens was another who voiced concern.
"11:50pm... I won't be one of them but how can you let the players play at 11am if you still dont have a schedule at this time?" she tweeted late Tuesday.
Top seed Iga Swiatek was among the lucky few to play on Rod Laver Arena with the roof closed, but said she felt for others less fortunate.
"I think it's really bad for the players that had to wait yesterday whole day here because it's really tiring, and they probably are going to have to stay another day on-site," she said.
"There's nothing I think the tournament organisers can do, but I'm surprised that they didn't put yesterday's matches earlier today on the stadiums, but I don't know how it works, honestly."
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