49 C.F.R. § 29.206
May the Department request and obtain an extension of time of the 45-day review period?
The Department may request an extension of time before the expiration of the 45-day review period. The Tribe may either grant or deny the Department's request for an extension. Any grant of extension of time must be in writing and signed by a person authorized by the Tribe to grant the extension before the expiration of the 45-day review period.