Where no limitation as to duration of the use was imposed at the time of authorization, such use may be continued.  Where such use was authorized subject to a term of years, such use may be continued until the expiration of the term, and thereafter, the agency which originally authorized such use may, in appropriate cases, extend the period of continuance for one or more terms of not more than 10 years each.  The agency may prescribe appropriate conditions and safeguards to minimize adverse effects of such use on the character of the neighborhood.