Visma Stämpla Chrome console script (quick & dirty) - worth noting is that you'll need to paste & run once every page load.

visma-stampla_greasemonkey.js

/* I'm not sure if this actually works in GreaseMonkey*, but something similar to this would be nice. */
var report = function(endDate) {
  if (!endDate) {
    console.error('No end date specified!');
    return;
  }
  var interval = setInterval(function() {
    if ($('#ctl00_maincontentholder_dayLabel').innerText.indexOf(endDate) !== -1) {
      console.log('Found', endDate, ', exiting...');
    	clearInterval(interval);
      return;
    }

    if ($('.editDayControl tr>td tr>td[colspan="3"]').innerText.indexOf('Ej schemalagd dag') === -1) {
      $('#ctl00_maincontentholder_IntervalsForm_startTextBox_TheTextBox').value = '08:00';
      $('#ctl00_maincontentholder_IntervalsForm_endTextBox_TheTextBox').value = '16:30';
      $('#ctl00_maincontentholder_IntervalsForm_AddButton').click();
    }

    setTimeout(function() {
      var a = $$('a');
      a[a.length -1].click();
    }, 100);
  }, 1000);
};

visma_stampla.js

(function() {
  if ($('.editDayControl tr>td tr>td[colspan="3"]').innerText.indexOf('Ej schemalagd dag') === -1) {
    $('#ctl00_maincontentholder_IntervalsForm_startTextBox_TheTextBox').value = '08:00';
    $('#ctl00_maincontentholder_IntervalsForm_endTextBox_TheTextBox').value = '16:30';
    $('#ctl00_maincontentholder_IntervalsForm_AddButton').click();
  }

  setTimeout(function() {
    var a = $$('a');
    a[a.length -1].click();
  }, 100);
});