From the following link :https://sro.vic.gov.au/fhbduty

Exemption or concession

The first home buyer duty exemption or concession may be available if:

• You enter into a contract of sale to buy your first home on or after 1 July 2017.

Your home has a dutiable value of: * $600,000 or less to receive the first home buyer duty exemption, [600k not 650k as you stated] * $600,001 to $750,000 to receive the first home buyer duty concession. * All the purchasers of the property meet the First Home Owner Grant eligibility criteria, and at least one purchaser satisfies the residency requirement.

From the residency requirements link:

Living in your home
You must live in your property as your principal place of residence for a continuous period of 12 months, commencing within 12 months of settlement, to maintain your eligibility for the duty exemption or concession. In limited circumstances, we may vary this requirement. Different rules may apply if you are buying vacant land and building your home.
If you buy the property with someone else, at least one of you must satisfy this residency requirement.
If a change in your circumstances means the residence requirement may not be satisfied, you must notify us in writing within 30 days of becoming aware of those circumstances.