I'm very much in the camp that the insurance must be paid for PRIOR to closing. I believe it goes beyond the risk that Dan presents. The regulation states:
A bank shall not make, increase, extend, or renew any designated loan unless the building or mobile home and any personal property securing the loan is covered by flood insurance for the term of the loan. [§339.3(a)]
The old Guidelines stated:
A designated loan must have flood insurance as a condition of closing. If a borrower will not voluntarily obtain coverage, the lender must deny the loan. [MPFIG – page 5]
If you close, advance the loan and then purchase insurance, how was the building "covered" (past tense). The Guidelines also use the terms "as a condition" - again, past tense.
Other than construction loans, there are no FAQs, regs, etc. that state anything about delaying the purchase.