start date for long term / short term capital gain determination

[Account Closed]

what is the reference date to determine long term / short term capital gains for a real property?

Is it the actual payment date? the sale contract date? or the vesting date?

I tried to look it up but found nothing conclusive

I read that stocks ownership starts at the moment of trade and not at the settlment date; so should i assume that the property's ownership starts at the payment date? 

I have a substantial time spread between the payment / sale contract and the vesting of a property i acquired and need to know from where i should start the 12 months count to fall into the long term capital gains