did you check the time differnce? Most customers are US/EU -
5:00 AM (5:00) Sydney Time = 8:00 PM (20:00) Previous Day Berlin Time
11:00 AM (11:00) Sydney Time = 8:00 PM (20:00) Previous Day New York Time
2:00 PM (14:00) Sydney Time = 8:00 PM (20:00) Previous Day California Time
as you are native english speaker .. us based should be best for you so best window is from 11:00 to 18:00 Sydney time.