Use detailed report view in toggl to find your avg focus-time for the day (or whatever range the report is showing)

timeMetrics.js

/**
 * I just paste this in my browser console when I'm curious. Nothing fancy ;) 
 *   it doesn't account for paging, which.... if it was that serious, I'd use the Toggl Api. 
 */
window.timeMetrics  = (function(){
  //-- get seconds worked from total (at the top of detailed report, at least)
  var parts = document.querySelector('.total-sum .duration')
    .outerText
    .split(':');
  //-- [hours, minutes, seconds]
  var seconds =
    (+parts[0]) * 60 * 60 +
    (+parts[1]) * 60 +
    (+parts[2]);
  //-- number of task items 
  var count = document.querySelectorAll('.time-entries-list > li').length;

  //-- math it
  return (seconds / count) / 60;
})()