Sydney Airport opening times are:
T1 International is open every day from 3AM to 11:00PM (0300 to 2300).
Customs opens for departures passenger processing at 4AM daily (0400).
T2 Domestic and the T3 Domestic Qantas terminal open every day from 4AM to 11:00PM (0400 to 2300).
There is a government mandated curfew operating at Sydney Airport between 11pm and 6am. For security reasons, the terminal is closed to the public overnight. During the times the airport is closed, there are a range of accommodation options on and off-airport from budget hotels to five-star establishments which may be booked online.
There are airport hotels located nearby Sydney Airport for travellers in transit.