For a non-HTTP specific phrase representing the same concept, I've tended toward "Time to first dopamine hit". :) That feeling of not being sure if a tool/API/

For a non-HTTP specific phrase representing the same concept, I've tended toward "Time to first dopamine hit". :) That feeling of not being sure if a tool/API/service/SDK/library/hardware is going to work for your purposes and then you get that first example/test/demo running and get your first response... "Ok, yep, this is good! Now is it gonna let me change this small thing so I can..." And the positive feedback loop has begun! It's definitely a metric that impacts developer adoption & is IMO something that needs to be routinely tracked in order to reduce the time taken to get started & catch any unexpected regressions.