able to check requester response time

It would be great if where able to check the requester response time, it's a great feature to have when there is a disscussion about the SLA agreement, where you can check and show why some incidents took longer then they should, especially when the requester took al long time to respond. In our SLA we have de clossure which says, that a ticket wil get on hold when a requster won't answer in 5 minutes to a ticket, so all the time after the 5 minutes isn't suitable for our SLA.