Our AGM always has a budget motion which sets the budget for the year and also states what the levy will be and when it will be due to be paid. I assume that something as basic as this is the same in every state or territory. In our case we have two half-levies due on specified dates usually 6 months apart.
If your last AGM resolved to have a quarter of the agreed levy due on each of four particular dates then that should be all the OC can levy on owners until it has had its 2015 AGM and resolved to levy some new amount (or the same amount) and specified the dates when specified portions of the 2015/16 levy would fall due.
This year our OC’s AGM was a bit later than usual for various reasons so the due date proposed by our EC for first levy payment was a bit later than usual also so that it would fall after the meeting. It would not have been possible to have that levy due before the 2015 AGM had given authority for that levy.
Where is your executive committee is all this? Having a strata manager is all very well and generally useful but the buck stops with the EC. If they are too timid they need to be told that they instruct the manager, not the other way around.