Start a nurture campaign when a form is submitted. Subsequent messages are sent relative to the date of the form submission.
These nurture campaigns aren't mutually exclusive and require careful planning of messaging (schedule). If your intent is to nurture prospects into leads by sending them a series of mutually exclusive emails you should use state based nurture emails instead.
How to add a nurture campaign to a form
Will contacts receive the same nurture series again?
If a contact is already part of this nurture campaign and there are messages scheduled to be sent later on then that contact will continue to receive emails as per their nurture schedule - the schedule will not restart.
If a contact is not currently part of a nurture campaign set on the form they will start receiving the emails from the nurture campaign from the beginning - even if they already received all emails from the same nurture campaign already.