; and (II) shall not prohibit or have the effect of prohibiting the provision, improvement, or enhancement of personal wireless service. (ii) Engineering standards; aesthetic requirements It is not a violation of clause (i) for a State or local government or instrumentality thereof to establish for personal wireless service facilities, or structures that support such facilities, objective, reasonable, and nondiscriminatory— (I) structural engineering standards based on generally applicable codes; (II) safety requirements (subject to clause (vi)); or (III) aesthetic or concealment requirements (unless such requirements prohibit or have the effect of prohibiting the installation or modification of such facilities or structures). (iii) Timeframes (I) In general A State or local government or instrumentality thereof shall grant or deny a request for authorization to place, construct, or modify a personal wireless service facility not later than— (aa) in the case of a request for authorization to place, construct, or modify a personal wireless service facility that is not a small personal wireless service facility— (AA) if the request is for authorization to place, construct, or modify such facility using an existing structure, including with respect to an area that has not previously been zoned for personal wireless service facilities (other than small personal wireless service facilities), 90 days after the date on which the request is submitted by the requesting party to the government or instrumentality; or (BB) if the request is for any other action relating to such facility, 150 days after the date on which the request is submitted by the requesting party to the government or instrumentality