Where 52/17 comes from
In 2014 the time-tracking company DeskTime looked at the top 10% of its users by productivity and found they worked in bursts averaging 52 minutes, then broke for about 17. The break was a real break: away from the computer. It is one company's data, not a controlled study, but the shape matches what other work on attention suggests: near an hour on, a substantial rest, repeat.
The important half
The 17 minutes. The productive users did not use them to check email. Leave the desk; the next block is armed when you come back and waits for you.