The filing of the registration form kicks off the 20 day “cooling off” period
During the 20 day cooling off period, the SEC registration form is transformed into a “preliminary” prospectus, which can be given to potential investors on a solicited or unsolicited basis.
To estimate demand for the IPO, the underwriter may solicit or receive indications of interest from potential investors during the 20 day cooling off period.
So the timeline is:
Create the syndicate and start the due diligence process
Prepare and submit the registration, triggering the cooling-off period
Create the red herring / preliminary prospectus from the registration
Distribute materials containing facts about the new issue and take indications of interest
Wait until the period is over to advertise or make sales
The only choice that happens before the cooling-off period is creating the underwriting syndicate.