1031 exchange on new construction short term rental

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With my 1031 I sold a commercial building and am purchasing a new construction short term rental. I did the 45 day identification and have an intermediary in place. I am going to be signing the purchase agreement for the replacement property and have the opportunity to save 3% by paying cash up front. Can the money being held be used at this time or can it only be given out at closing. I believe I could use money for down payment,  earnest money etc. But, could it all be used to pay up front before construction?