I consider to use the start and not the finishing for the calculation. And if a building uses a decade to get finished then it is even worse.
A lil like buying a Car here, paying a Years Comprehensive Insurance and Registration in advance, then waiting 12 months for your Plates to arrive so you can start driving it to avail yo... Wait... Renew your unused Insurance and Registration only to start all over again? "You're Welcome Sir"
At least you can move into your home immediately and don't have to wait 12 months to do it. Except you pay something in a presale which is not yet constructed. (A rule tells: Never buy anything that is not existing and complete.) This car and plates mess is one case why I'm looking for a place with reliable public transportation.