Baba, from the circular:

"In the event that the full payment cannot be made by December 31, 2019, the Company will either negotiate additional time for the payment or seek some other arrangement with DL-Shanghai or its investors in order to conclude the sale. In the circumstance that the parties cannot conclusively agree on terms for the sale of DenseLight by June 30, 2020, the shares in escrow will be returned to POET."

So, there is a mechanism in place to complete the sale if the money is delayed beyond Dec 31.  Maybe just covering all of the bases, but my concern with this is that it does give the buyer an opportunity to stall or delay payment if they want to....