Lumovest - get course total time

script.js

function display (seconds) {
  const format = val => `0${Math.floor(val)}`.slice(-2)
  const hours = seconds / 3600
  const minutes = (seconds % 3600) / 60

  return [hours, minutes, seconds % 60].map(format).join(':')
}

// The magic
display([...document.querySelectorAll('.lesson-time')].
        map((el) => el.textContent.split(':').
        reduce((acc,time) => (60 * acc) + +time)).
        filter(Number).
        reduce((a,b) => a + b, 0));