First response measures acknowledgment
First response time measures the interval between a customer's request and the first meaningful reply. It is useful because silence creates uncertainty. A quick response confirms that the request has entered the system and sets expectations for what happens next.
Resolution measures completion
Resolution time measures how long it takes to restore service, solve the issue, or complete the request according to the agreed definition of done. This metric is closer to the customer's end-to-end experience, but it can be influenced by complexity, parts, third parties, approvals, and customer availability.
Read them together
A team can have excellent first response time while resolution remains poor if the first reply is only a fast acknowledgment. The opposite can also happen: technicians solve issues quickly but customers feel ignored because communication is late. Strong service needs both progress and visibility.
Key idea
Do not optimize response time until replies become meaningless. Do not optimize resolution time by hiding waiting periods. Measure what the customer actually experiences.