This is a major area of mistake when it comes to DIY tax solutions. Sometimes its the date of settlement and sometimes its the date you contract to buy it. For a new build it can even be the date construction commences.
If its a house and land then there may be two CGT assets. If you own the land for two years and contract a builder and he completes it and its promptly then there may be no discount on part of the sale. And an apportionment issue. Lots of factors.
This is an area where personal advice counts.