Section 8. Before adopting any rule or regulation under section six, a public hearing shall be given, and not less than ten days before the hearing a notice thereof shall be published in at least three newspapers, of which one shall be published in Boston. Such rules or regulations, when approved by the associate commissioners and the assistant commissioner, shall, subject to section thirty-seven of chapter thirty, take effect thirty days after such approval or at such later time as the associate commissioners and the assistant commissioner may fix. Before adopting any order a hearing shall be given thereon, of which a notice of not less than ten days shall be given to the persons affected thereby.