Mich. Comp. Laws § 257.1317: Inspection; "reasonable business hours" defined.

Sec. 17.

(1) The owner of a facility that is registered or is required to register under this act shall ensure that the facility and, if applicable, any auxiliary facilities are open to inspection by the administrator and other law enforcement officials during reasonable business hours. During reasonable business hours, the administrator and other law enforcement officials may make periodic unannounced inspections of the premises, parts records, and parts inventories of a facility or auxiliary facility.

(2) A person shall not hinder, obstruct, or otherwise prevent an inspection under this section or section 18 or 18a.

(3) As used in this section, "reasonable business hours" includes any posted or advertised business hours of a facility.