In Victoria for State offences after being arrested for questioning you must be either released on bail or brought before a bail justice or Magistrates Court within a “reasonable time”. That period is not defined at all in the Crimes Act.
Obviously each case turns on its own circumstances as to what is reasonable. While being held a person must have their rights explained to them and it must be explained as to the circumstances of the offence in sufficient detail to be meaningful.
The Courts have a discretion to exclude interviews which were obtained unfairly or improperly and the length of time held is one factor in deciding whether to exclude an interview.
For Federal offences if you are arrested or treated as being arrested there is a limit of 4 hours detention or 2 hours if a child under 18. These, as with much the Feds do, do not provide real protection. There are a number of periods of time that are excluded from the time calculation if the interview has been delayed or suspended. They can apply for an extra 8 hours if they want to.