PER T1 (main international terminal) is 24 hrs but the limited QF international flights (SIN, LHR, CDG, FCO and soon JNB) operate from the T3/T4 (Domestic/International) precinct and do appear to have a couple of hours gap in ops between 1am and 3am (or thereabouts). That would normally only affect QF72 from SIN if it was running late.