When to pay transfer duty

You must pay transfer duty within three months of signing a contract for sale or transfer, except in the case of off-the-plan purchases.

If you buy off-the-plan and you intend to live in the property, you may be able to defer your transfer duty liability for up to 12 months.

Read more on link: https://www.revenue.nsw.gov.au/taxes-duties-levies-royalties/transfer-duty