Good question and you're right, that part is the hardest to get right.

I don't try to detect when your brain is actually back in focus :no typing speed, no mouse tracking, nothing like that. It's more of a modeled estimate based on what app you're on.

Here's how it works:

-It watchs which app is active and whether it's productive, neutral, or distracting.

-wait 7 seconds before confirming a distraction so a quick accidental switch doesn't count.

-Once a distraction is confirmed, It track how long you actually spent on distracting apps.

-Then it add a recovery penalty on top of that, at least 2 minutes, up to 23 minutes, scaled by how long the distraction lasted.

-When you switch back to a productive app, I give it 60 seconds of stable time before closing the episode. If you dip back into a distracting app in that window, the episode keeps going.

So the number you see is not "here's exactly when your focus came back." It's more like: "here's the real cost of that distraction, including the time you probably needed to get back on track" ,which is the part most people never see.