My understanding is that the general rule is maximum 45 days from application for "minor projects", maximum 90 days for "major projects", or 60 days from public hearing (if applicable).
The amount of time it takes to get a permit varies according to many factors, including what type of permit it is, its complexity, who the permitting authority is, how controversial the project is, and whether the permit is appealed after issuance. A New Source Review permit issued by EPA takes between six months and one year. The time frame for NSR permits issued by state and local air pollution control agencies varies, and is often specified in local regulations. In California, state law requires agencies to issue NSR permits within 180 days.
For Title V, federal regulations say that a permitting authority must issue all of its permits within three years of the date that the agency's Title V program became effective. One third of the total number of permits are supposed to be issued each year. However, most agencies are behind schedule. In addition, issuance can be delayed if EPA, on its own initiative or as a result of a citizen request, objects to a permit. Thus the amount of time it takes to get a Title V permit depends on agency specific time frames and circumstances that are often beyond the applicant's control.
Region 9: Allegany, Chautauqua, Cattaraugus, Erie, Niagara and Wyoming counties http://www.dec.ny.gov/about/619.html NYSDEC Region 9 Office 270 Michigan Avenue Buffalo, NY 14203 (716) 851-7200 Hours: 8:30 AM to 4:45 PM, Monday through Friday