According to the Act:
initial period, in relation to an owners corporation, means the period commencing on the day on which that owners corporation is constituted and ending on the day on which there are owners of lots the subject of the strata scheme concerned (other than the original owner) the sum of whose unit entitlements is at least one-third of the aggregate unit entitlement.
In other words, the initial period ends when one-third of units have been sold (give or take a few big or little ones to make up the one-third of Unit Entitlements). The developer then has two weeks in which to call the first AGM.
Importantly, at that point the voting power of the developer is reduced to one-third of their holding until such times as they have sold more than half their units. Also, the developers are restricted in contracts that they can sign in this initial period as they all have to be approved (or not) by the owners at the first AGM.