The quiet period begins when the registration statement is made effective and lasts for 40 days after the stock begins trading. Its purpose is to create a level playing field for all investors by ensuring everyone has access to the same information.

https://www.investopedia.com/terms/q/quietperiod.asp

However, a quiet period extends from the time a company files a registration statement with the SEC until SEC staff declare the registration statement "effective." During that period, the federal securities laws limit what information a company and related parties can release to the public.

https://www.sec.gov/fast-answers/answersquiethtm.html