Revenue recognition

Calibra co. builds apartment blocks which takes 2 years to complete from the date of signing the contract.The title,possession and therefore control passes after construction completion.The price payable on completion of each apartment is $9.55 million.
Alternatively, customers pay $8.5million cash on the day contract is signed.Accountant figured the borrowing rate @ 6% for Calibre co. Calibre co. immediately recognises $8.5 million as revenue if customers pay when they sign the contract.

My que is how should we recognise the revenue? Should we recognise contract liability on signing of contract.Later we recognise 425000 each year and record interest income every year.