Queensland: certificate or Form 36
In QLD you generally need a current pool safety certificate before settlement. Certificates are issued by QBCC-licensed inspectors and last 2 years for a non-shared pool (1 year for shared pools).
No certificate? You can give the buyer a Form 36 notice before settlement instead. That transfers the obligation: the buyer then has 90 days from settlement to obtain a certificate - at their cost, but any barrier problems become their problem to fix too. Selling at auction? The Form 36 must be given to bidders before the contract is signed.
New South Wales: certificate on the contract
In NSW, the sale contract must include one of: a certificate of compliance (valid 3 years, from council or a private E1-accredited certifier), a relevant occupation certificate less than 3 years old, or a certificate of non-compliance. Your pool must also be on the NSW Swimming Pool Register.
The certificate of non-compliance works like QLD's Form 36 - it passes the obligation to the buyer, who gets 90 days from settlement to fix the barrier and obtain compliance. Note: this regime doesn't apply to lots in strata or community schemes with more than two lots, or to off-the-plan contracts.
Victoria: certificate lodged with council
Victoria doesn't hang its rules off the sale - your pool or spa must be registered with council and hold a certificate of barrier compliance on its 4-year cycle regardless. Buyers (and their conveyancers) will ask for evidence that the pool is registered and its certificate is current, and an overdue certificate discovered mid-sale can stall settlement while an inspection and fixes are arranged.
Other states
In SA, safety features must be brought up to standard before title transfers on older pools - build that into your campaign timeline. In WA, TAS and ACT there's no certificate-to-sell requirement, but the barrier must still comply and buyers' building inspectors will flag defects. In the NT, a compliance certificate (or acknowledgement notice for older pools) applies when a property sells or leases.
Timing: when to book the inspection
Book the inspection when the property is listed, not when a contract lands. The maths is simple: inspection availability (a few days to a week), plus fixes if it fails (days to weeks depending on the trade), plus re-inspection. Around 1 in 2 pools fails something on the first pass. An early certificate is also a selling point - agents list it in the campaign.
A missing certificate discovered a week before settlement is one of the most common causes of delayed pool-property settlements. Fixes plus re-inspection rarely happen inside a week in summer.