AUG 28Your GST return and payment is due for the taxable period ending 31 July.
SEP 28Your GST return and payment is due for the taxable period ending 31 August.
OCT 28Your GST return and payment are due for the taxable period ending 30 September. (This is an extension of the usual 28 October due date.)
When they're used
A GST-registered seller can issue a single tax invoice when supplying multiple goods or services to the same buyer.
A common example is an invoice for the monthly rent of commercial premises.
You must identify each supply separately on the tax invoice, but you do not need to show the separate GST amounts. You can just show the GST for the total supply.
Here's an example of a tax invoice for multiple supplies.