Any regulation or provision of this chapter may be changed and amended from time to time by the City Council; provided, however, such changes and amendments shall not become effective until after study and report by the Commission and until public hearings have been held by both the Planning and Zoning Commission and City Council, public notice of which shall have been given in a newspaper of general circulation in the City at least ten (10) days but not more than twenty (20) days prior to such hearing.