Hi de nero
As your question relates to the sale of a capital asset, the ATO takes the view that the period of time of ownership runs from date of contract to buy through to date of contract to sell.
In this instance you are the vendor.
The date on which the purchaser makes their first offer to buy from you is the date of the contract. They have stated their intention to buy and although negotiations may stretch on for days or even weeks, the date they have offered to buy is the date of the contract.
The date that you accept the offer and the date of exchange of the contracts are secondary to the initial date.
Not all contracts must be in writing, but under the various Instruments Acts contracts for the sale of property must be in writing.
Many a vendor has been 'caught out' by putting their property on the market within the first twelve months of ownership, thinking that they will be eligible to discount the capital gains by the 50% rule after a year and a day, with the relevant date being that of settlement. However, due to the date of the contract of sale being the date on which capital gains is assessed can mean missing the discount, but more importantly incurring a capital gain and therefore tax on the gain in the current tax year. Oops!
Check the ATO website, there are lots of practical examples of how this all works. It is their rules, after all, so may as well play the game in the standard format.
Hope this helps
Kristine