Checking freebusy on all Google Calendars for an authorized account.

all-calendar-freebusy-check.php

<?php 

  // Create an authorized calendar service object
  $calendarService = new Google_Service_Calendar( $client );
  $calendarList = $calendarService->calendarList->listCalendarList();
  $calendarArray = [];
  
  // Put together our calendar array
  while(true) {
      foreach ($calendarList->getItems() as $calendarListEntry) {
          $calendarArray[] = ['id' => $calendarListEntry->id ];
      }
      $pageToken = $calendarList->getNextPageToken();
      if ($pageToken) {
          $optParams = array('pageToken' => $pageToken);
          $calendarList = $calendarService->calendarList->listCalendarList($optParams);
      } else {
          break;
      }
  } 
  
  // Make our Freebusy request
  $freebusy = new Google_Service_Calendar_FreeBusyRequest();
  $freebusy->setTimeMin('2015-06-01T00:00:00-04:00');
  $freebusy->setTimeMax('2015-06-05T00:00:00-04:00');
  $freebusy->setTimeZone('America/Eastern');
  $freebusy->setItems( $calendarArray );
  $createdReq = $calendarService->freebusy->query($freebusy);
  
  // You will see each calendars and if there are any 'busy' items returned between the dates set.
  var-dump($createdReq);