Response is the maximum amount of time for us to respond and in our world that means assign a tech to the case and start work (unlike other who class this as the time to send an email acknowledgement)

The TTR can be time specific, so that you may have an SLA that mandates a TTR of 1 hour Monday to Friday 0900-1800, but 4 hours outside of that window.

The smallest TTR is 1 hour, and this is covered in SLA10+