Indiana Code Title 5. State and Local Administration § 5-1.3-1-8

Sec. 8. (a) An action to contest the validity of any action taken under this article may not be brought after the fifteenth day following the date the resolution of:

is adopted approving the action taken, provided the applicable statutory procedures have been completed.

(b) If an action challenging an action taken under this article is not brought within the time prescribed by this section, the lease, contract, bonds, notes, obligations, or other action taken shall be conclusively presumed to be fully authorized and valid under the laws of the state and any person is estopped from further questioning the authorization, validity, execution, delivery, or issuance of the lease, contract, bonds, notes, obligations, or other action.