Google App Script for calculating free time across multiple Google calendars. Writes results to a Google spreadsheet so they can be plotted.

gistfile1.txt

function startCounting() {
 // create 5min Trigger
  ScriptApp.newTrigger("countEvents").timeBased().everyMinutes(5).create(); 
  
  // create end Trigger
  //var end_date_trigger = new Date(end_date_array[2], end_date_array[1] - 1, end_date_array[0], 10);
  //ScriptApp.newTrigger("stopCounting").timeBased().at(end_date_trigger).create();
}

/* remove all triggers when it comes to the end of a Sprint */
function stopCounting() {
  var triggers = ScriptApp.getScriptTriggers();
  for (var i = 0; i < triggers.length; i++) {
    ScriptApp.deleteTrigger(triggers[i]);
  }
}

/**
  * It would count FULL hours that did not have any events set between 7am and 6pm 
  * and it would tell me how many there were.
 */
function countEvents() {
  var sheets = SpreadsheetApp.getActiveSpreadsheet().getSheets(),
    active_sheet = "",
    sprint_info_column = 10;
  
  for (var i=0; i<sheets.length; i++) {
    if (sheets[i].getName().indexOf("#active") != -1)
      active_sheet = sheets[i].getName();
  }

  var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName(active_sheet);
  
  var baserow = 2,
      basecolumn = 1;
  var start_date_array = sheet.getRange(3, sprint_info_column).getValue().split("."),
      end_date_array = sheet.getRange(4, sprint_info_column).getValue().split(".");
  var start_date = new Date(start_date_array[2], parseInt(start_date_array[1])-1, parseInt(start_date_array[0])),
      end_date = new Date(end_date_array[2], parseInt(end_date_array[1])-1, parseInt(end_date_array[0]));
  var current_date = new Date(start_date.getTime());
  
  // generate headers
  sheet.getRange(baserow - 1, basecolumn + 1, 1, 1).setValues([['Hours Free']]);
 
  //create calendards
  var cals = new Array();
  cals.push(CalendarApp.getDefaultCalendar());
  cals.push(CalendarApp.getCalendarById('[calendar id]'));
  //travel calendar
  cals.push(CalendarApp.getCalendarById('[calendar id]'));
  
// generate dates
  var row = baserow;
  while (current_date.getTime() != end_date.getTime()) {
    sheet.getRange(row, basecolumn, 1, 1).setValue(current_date.getDate() + "." + (current_date.getMonth()+1) + "." + current_date.getYear());
    current_date.setDate(current_date.getDate() + 1);
    row++;
  }
  sheet.getRange(row, basecolumn, 1, 1).setValue(current_date.getDate() + "." + (current_date.getMonth()+1) + "." + current_date.getYear());
 
  //find hours
  var now = new Date(start_date.getTime() + (7 * 60 * 60 *1000));

  for (var j = 0; j < 5; j++ ) {
    beginningOfDay = new Date(now.getTime() + (j * 24 * 60 * 60 * 1000));
    endOfDay = new Date(now.getTime() + (j * 24 * 60 * 60 * 1000) + (10 * 60 * 60 * 1000));
    
    Logger.log('beginning: ' + beginningOfDay);
    Logger.log('end: ' + endOfDay);
    
    /* presumed time budget:
       10 hour day
       minus 1.5 hours for email
       minus 1 hour for break
       minus 1 hour for travel time to and from campus
       = 6.5 hours
    */
    totalHours = 6.5; 
    
    for (var i = 0; i < cals.length; i++) {
      var events = cals[i].getEvents(beginningOfDay, endOfDay);
      
      Logger.log('Number of events in cal ' + i + ': ' + events.length);
      
      for (var k = 0; k < events.length; k++) {
        //TODO: improve exclusion of events I have declined by checking for alternate
        // email ids
        if (events[k].isAllDayEvent() == false && events[k].getMyStatus() != CalendarApp.GuestStatus.NO) {
          Logger.log(events[k].getTitle());
          var start = events[k].getStartTime();
          var end = events[k].getEndTime();
          Logger.log(start);
          Logger.log(end);
          var eventLength = ((end - start)/ (60 * 60 * 1000));
          Logger.log("length: " + eventLength + " hours");
          totalHours = totalHours - eventLength;
             
        }
      } 
    }
    sheet.getRange(baserow + j, basecolumn + 1, 1, 1).setValues([[totalHours]]);
   }
  
   
};