Need help filtering a column to see only "duplicate" entries

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Hello everyone,

This is my first topic here, if anyone has a solution to my problem I'd be forever grateful. 

I would like to create a report to see "duplicate tickets", meaning tickets that have been created several times instead of just once, by one person. So how could I filter out just the tickets that are created by one person in like let's say a less by 5 minute interval, if that makes sense?

I have the following data available:
incidents.ref_no - the unique identifier of the ticket

contacts.email - the e-mail address of the person that created the ticket