Hi Fraser,
Sorry for the confusion.
Please refer to the following section to know more about recurring journey.
Set up a recurring journey
A Customer Journey can be seen as a one-way pipeline, which means that even if a contact submits a form multiple times, it will still be treated as the same contact and can only be processed once for subsequent steps. The only way to get contacts back into this pipeline is to set the journey to a recurring one.
But the Recurrence interval needs to be at least one day.
So if in your requirements you have contacts submitting the same form multiple times in one day, then customer journey cannot accommodate sending an email for each submission and therefore you need to find another way.
If you don't have formatting requirements for submitting reminder emails and just need a notification, you could consider creating a Flow to trigger this by submitting to send a regular email to the contact.