Long term capital gain tax exemption

For Long Term Capital Gain tax exemption, investment is required to be done within 2 years after sale of asset.

My query is:

1) This 2 year period is calculated from date of Sale Deed or date of Agreement to Sale?

2) With reference to the new investment required for tax examption, is it required that possession of new property should be gained within 2 years or only "Agreement to Sale" is sufficient for this purpose & possession can be taken later anytime; or even agreement to sale can be beyond 2 years but physical payment should be made?

Thank you all in advance for your comments!