How much time should we allow between an international arrival and a separate Sydney domestic flight?

Check the airline's current bag-drop deadline and change policy. If the tickets are separate, the second airline may have no obligation to rebook you after a missed connection.

Book a later domestic flight if the price difference is tolerable. A small delay to the international arrival could make an apparently generous two-hour gap unusable.

Treat the connection as two separate journeys. Allow for immigration, baggage, customs, the terminal transfer, a new bag drop and security before the domestic cutoff.