codeigniter内的Google REST调用失败

I've got a REST call to my Google calendar that works out fine on my old website (www.gmbc.org/events.php), but when the identical call is made from a codeigniter controller, the timeMin / timeMax options cause it to throw a 400 at me (remove them, and the call successfully retrieves the whole calendar from 2012):

    $st_date = date(DateTime::ATOM);
    $end_date = date(DateTime::ATOM, time()+(31 * 24 * 60 * 60));
    $call_url = 'https://www.googleapis.com/calendar/v3/calendars/calendar%40gmbc.org/events?timeMin='.$st_date.'&timeMax='.$end_date.'&singleEvents=true&orderBy=startTime&key=[mykeythatworksjustfine]';

    $events_call = $this->curl_get($call_url);

echoing $call_url confirms it's being created identically, and print_r-ing the result confirms it's reaching google:

stdClass Object (
[error] => stdClass Object (
  [errors] => Array (
    [0] => stdClass Object (
      [domain] => global [reason] => badRequest [message] => Bad Request )
    )
    [code] => 400 [message] => Bad Request
  )
)

...what could possibly be going on? Does codeigniter interfere with the curl call?

I am able to successfully retrieve events from this calendar with TimeMin and TimeMax set using the API explorer: https://developers.google.com/apis-explorer/#p/calendar/v3/calendar.events.list?calendarId=calendar%2540gmbc.org&timeMax=2014-11-30T00%253A00%253A00Z&timeMin=2014-10-01T00%253A00%253A00Z&_h=2&

The query it's sending is: GET https://www.googleapis.com/calendar/v3/calendars/calendar%40gmbc.org/events?timeMax=2014-11-30T00%3A00%3A00Z&timeMin=2014-10-01T00%3A00%3A00Z&key={YOUR_API_KEY}

Try making sure the query you are sending from PHP ends up the same.