Capital gains tax

Pl clarify if period of holding of a property is calculated from date of payment or registration of property. I had paid the full amount (except for stamp duty and registration) towards an under construction residential flat in January 2013. If I sell it as soon as I get possession (in a couple of months) will the gains be subject to long term or short term capital gains tax? If subject to STCG tax, can I set off the gains by investing in another property or capital gains bonds?