Tracking new lead response time

Tracking new lead response time

Hi,

I have a team of Sales Development Reps, who have a KPI of responding to a lead within 20 mins or less once it hits the system.  I seem to recall that Zoho CRM had the capability to track this in a previous version, but don't see it anywhere.  

It's great that the system tracks lead conversion time, but how am I supposed to make sure that my SDR's are picking up leads in a expeditious manner?

Any suggestions?