A premium finance company may, upon agreement with the insured, extend the scheduled due date or defer the scheduled payment of all or any part of any installment or installments payable thereunder. The agreement for such extension or deferment must be in writing and signed by the parties. The premium finance company may charge and contract for the payment of an extension or deferral charge by the insured and collect and receive the same; but such charge may not exceed an amount equal to 1 percent (1%) per month simple interest on the amount of the installment or installments, or part thereof, extended or deferred for the period of extension or deferral or $1, whichever is the greater amount. The period shall not exceed the period from the date when the extended or deferred installment or installments, or part thereof, would have been payable in the absence of an extension or deferral, to the date when the installment or installments, or part thereof, are made payable under the agreement of extension or deferment.