Frontend & browser·Performance and Core Web Vitals
the lab report says two seconds of blocking time and you can see it as a wall of yellow in the profile.
Total blocking time
Also calledTBT
The sum of the part of every long task that exceeds fifty milliseconds, between first contentful paint and interactivity. It is the lab stand-in for responsiveness, because a synthetic run has no real interactions to measure. Improving it and improving interaction to next paint usually mean the same work, which is why it is the number to watch in CI.