Reply Time metrics after assigning to different group

I'm looking for a way to measure the response time after a ticket is assigned to a different group. 

Currently a ticket arrives and is assigned to Group 1 with default SLA policy applied. First Reply Time is measured and that works fine. However, the ticket may need to be escalated and assigned to Group 2, and I want to know if the same metrics can be measured once it's been assigned to the new group, those metrics being, wait time, reply time.