Filter on call duration in reporting analytics

We need a filter based on call duration in our reporting analytics. This is to assess our sales team's performance with regards to how long they've been on a call with a lead. We want to see how many calls that went longer than 30 sec ended up converting (we'll check this on our CRM, just need the list of leads that were in conversation with our sales agents for more than a certain amount of time). This is our criteria of a 'good call'.