Before the Planning Commission shall, by proper action, formulate its recommendation to the Governing Body on any such proposed or requested change of zoning district boundary or regulations, whether initiated by the Governing Body or Planning Commission or by others, the Planning Commission shall hold a public hearing on such proposal. The secretary of the Planning Commission shall cause a notice of public hearing to be published once in the official newspaper and at least 20 days shall elapse between the date of such publication and the date set for the hearing. Such notice shall fix the time and place for such hearing and shall contain a statement regarding the proposed changes in the regulations or restrictions or in the boundary of any district, and if such proposed amendment will affect specific property, the legal description and general street address shall be given; provided that, in addition to such publication notice, at least 20 days before the hearing written notice of such proposed change shall be mailed to all the owners of land within the city boundary located within 200 feet of the area proposed to be altered, except that where the change will include property located adjacent to or outside the city's limits, the written notice shall also be mailed to all owners of land outside the city's boundary located within 1,000 feet of the area proposed to be altered. Failure to receive such notice shall not invalidate any subsequent action taken when the notice has been properly addressed and deposited in the mail. In addition, where such proposed change is in regard to a specific property, a notice of such hearing shall be posted in a conspicuous manner on the subject property at least 20 days prior to the hearing.