The Prompt Payment Act of Nineteen and ninety-seven requires government agencies to pay their bills on time.
See- National Public Accountant, Jan. 1997, article by Lampert and Wilson.
A form, OMB No. 3090-0105, provides "Contractor's Request for Progress Payment."
For most payments, see "Financial Manual for Grants and Contracts."

Act sections provide for government contract financing "in terms of partial payments, progress payments, guaranteed loans and advance payments for contracts other than cost-reimbursement contracts."
See FAR, Part 32.

Donals sky-is-falling warning seems to point to what has been government policy for years- if a contractor has a good plan but cannot finance it all up front, the government helps out.
As far as I can determine, the OMB has never had a set minimum payment system.