Gifting a property - effective "sale" date

Hello, We are about to gift a leasehold property to a family member. What would be the "effective sale" date / property disposal date? Is it when the parties sign the transfer contract? Or when the transfer has been sent to the Freeholder? Or when the family member moves in and takes responsibility for the Council Tax, Ground Rent and Service charge? Or is it only once it has been registered with LR? (This is to understand if the property disposal would fit into the 3-year timeframe for the Stamp Duty rebate). Many thanks, M

Hi,
The effective date will be when the new owner basically has the keys to move in.
Thank you.