Hi @adam_cannon_23 ,

Create a response SLA definition.

Start condition should be like, active is true and assigned to is empty.

Stop condition is active is true and assigned to is not empty.

If you create a 24/7 SLA duration, then you will be able to see how long time the SLA has been running. 

If my answer has helped with your question, please mark my answer as accepted solution and give a thumb up.

best regards

Anders