There are actually no timeframes within which a planning permit must be decided. Under the Planning & Environment Act 1987 planning permit applicants are able to make an appeal to VCAT if their application has not been determined within 60 statutory days of the date of lodgement.
The number of days are not calendar days, but statutory days because the clock turns on and off at different times where, for example, further information is sought from the applicant, or in other specific circumstances.
The length of time to assess an application will vary depending on whether a pre application meeting has been held with a Council planner, the quality of the application, the complexity of the proposal, the number of referrals required, whether it is required to be advertised, and whether any objections are received.