This really belongs in IMHO. Your answer is that you should consult with your tax lawyer or accountant to do this correctly.
If you are dealing with real property, from the time you sell your old property you have 45 days to identify the property you want to buy and 180 days to complete the exchange for a Section 1031 tax free exchange. When you identify the property you want to buy, you have to give notice to an appropriate person within the 45 days. When you sell your original property, you have to keep the funds with a “qualified intermediary or other exchange facilitator” in the words of the IRS. We have no idea if you did those things, so we can’t tell you whether you can still reasonably claim to be completing a Section 1031 exchange. If you have done everything correctly so far, and you actually complete the 1031 exchange correctly, you will report the Sec. 1031 exchange for the 2016 tax year (i.e., with the tax return you file in 2017).
If you don’t complete your 1031 exchange correctly, you have to recognize the gains in 2015. You can file an extension on your 2015 tax return to get more time to file if you need more time to figure out if you’ll get the exchange done in time. But, the general rule is that you must pay your 2015 tax liability by the “April 15th” deadline (actually, it’s April 18, 2016 for year 2015 returns). That means if you don’t expect to get your exchange done on time, you should pay the taxes on the gain by the tax filing filing deadline. If you do expect to make the exchange on time but you later fail to do so, you will have to amend your 2015 return and possibly pay penalties for late payment of taxes.