This response is based on the information provided.  We suggest you discuss with your contracting team, financial team, program manager and/or legal department as appropriate. 

The contract clauses specify payment terms.  In general the payment is what the contract calls for.  A construction contract will likely have FAR 52.232-5, Payments under Fixed-Price Construction Contracts, and FAR 52.232-8, Discounts for Prompt Payment.  If a contractor offers "net terms" DFAS will determine which is more favorable to the government.

"If your invoice offers discount terms better than those specified by the contract, we will take the better of the terms offered. You may offer a discount on your invoice even though the contract terms are net 30 days."

(DFAS  --  Contractor and Vendor Payment Information Booklet, PG 13; April 4, 2018).