But you are right - If the burdens and benefits of ownership substantially transfer to the buyer the sale can be deemed to have happened upon execution of the contract rather than with deed passing.So, your 1031 can start with the signing of the contract and delivery of the down payment. 

I have managed my own rentals and in each state there were different timelines and notices that needed to be delivered and delivery methods.  

So what this price reflects is future delivery contracts for lumber for the month of September in the amount of 1000 board feet.

Although, I do appreciate the advice and warnings from anyone, the delivery from some of the commenters was a little much. 

I am also the one buying and delivery the materials.

USPS and other delivery guys mostly deliver mail at one location only near mailboxes, but in once in a while some case Prime or different delivery person will drop packages outside the building also, because they may not have access code to the building.

The neighboring building owner hates that we have deliveries 6 days per week and that we have trash cans at the rear of the building.

Florida's financing extension is in paragraph 5: EXTENSION OF CLOSING DATE:(a) If Paragraph 8(b) is checked and Closing funds from Buyer's lender(s) are not available on Closing Date dueto Consumer Financial Protection Bureau Closing Disclosure delivery requirements ("CFPB Requirements"),then Closing Date shall be extended for such period necessary to satisfy CFPB Requirements, provided suchperiod shall not exceed 10 daysAlso, if the financing period passes and the buyer's don't opt out, this would apply: v) If Buyer is unable to obtain Loan Approval after the exercise of diligent effort, then at any time prior toexpiration of the Loan Approval Period, Buyer may provide written notice to Seller stating that Buyer has beenunable to obtain Loan Approval and has elected to either:107 (1) waive Loan Approval, in which event this Contract will continue as if Loan Approval had been obtained; or108 (2) terminate this Contract.

First time the reason was, "Unable to access delivery location", second time, "Unable to deliver due to animal interference". 

It is cleaner, more efficient and you avoid delivery which can be a pain if they forget to deliver.