Colo. Rev. Stat. § 29-8-121
Failure to pay the whole assessment within said period of thirty days shall be conclusively considered to be an election on the part of all persons interested, whether under disability or otherwise, to pay in such installments. In case of such election, the assessment shall be payable in equal annual or semiannual installments of principal, the first of which installments shall be payable as prescribed by the governing body, and the last installment within not more than twenty years, with interest in all cases on the unpaid principal, payable annually or semiannually at a rate not exceeding the maximum net effective interest rate authorized by the governing body. The number of installments, the period of payments, the date of the initial payment, and the maximum net effective interest rate shall be determined by the governing body and set forth in the resolution required by section 29-8-115.
C.R.S. § 29-8-121