Okla. Stat. tit. 19, § 19-1249: Due date of first installment - Delinquent installments -

Collection of installments - Limitation of actions.

The first installment of the assessment, together with interest

upon the whole assessment from the date of the passage of the

assessing resolution to the first day of the next September, shall

be due and payable in cash on or before the first day of September

next succeeding the passage of the resolution. If such assessing

resolution is not passed prior to the first day of July, the first

installment of such assessment shall be due and payable in cash with

interest from the date of the passage of such assessing resolution

to the first day of September of the following year. In case any

installment or interest is not paid when due, the installment so

matured and unpaid and the unpaid interest thereon shall draw

interest at the rate of fifteen percent (15%) per annum from

maturity until paid, except otherwise provided. All assessments and

interest shall be collected by the county clerk and shall be paid to

the county treasurer who shall keep the same in a separate special

fund for the purpose of paying the bonds and interest thereon,

issued against such assessments. After the payment of all bonds and

interest thereon, any surplus remaining in said fund shall be used

for the purpose of repairing and maintaining any improvement for

which assessments have been levied, and for no other purpose. No

statute of limitations shall commence to run against any installment

until after the maturity of all installments.