Short answer: Rare and risky. Needs written tenancy agreement. Most wait for settlement. Get insurance if you do.
Sometimes, if the seller agrees. You sign a separate tenancy agreement and pay rent until settlement. This is rare and risky. If settlement fails, you have tenancy rights but not ownership. Most buyers wait for settlement. Do not move in early without a written agreement and insurance.
Settlement Date: 30 June
Early Move In: 15 June
Rent: $400/week until settlement
Risk: Settlement delayed, you are now a tenant not owner