Why does Cloud Tasks gives "Deadline Exceeded" error after 60s?

Question

I'm using google-cloud-tasks==2.2.0 with Flask Gunicorn. This is how I send a task to a queue:

def send_task(payload, queue, uri, *args):
    url = f'https://www.mywebsite.com/{uri}'
    payload = json.dumps(payload)
    payload = payload.encode()
    parent = client.queue_path(project=project, location=location, queue=queue)
    service_account_email = 'myaccount.com'
    # Construct the request body.
    td = '1800s'
    duration = duration_pb2.Duration()
    time = duration.FromJsonString(td)

    now = datetime.utcnow() + timedelta(seconds=10)
    ts = timestamp_pb2.Timestamp()
    now = ts.FromDatetime(now)

    task = {
        'http_request': {  # Specify the type of request.
            'http_method': tasks_v2beta3.HttpMethod.POST,
            'url': url,
            'body': payload, # Convert dictionary to string
            'headers': { # Add custom header
                'Content-Type': 'application/json'
            },
            'oidc_token': {'service_account_email': service_account_email}
        }
    }
    task['schedule_time'] = now
    task['dispatch_deadline'] = time
    response = client.create_task(request={"parent": parent, "task": task}, timeout=30.0)

I use dispatch_deadline which is supposed to support 30 minutes timeout, using this API reference.

But no matter how I try, my task fails after 60 seconds with 504 DEADLINE_EXCEEDED error.

Honestly, is this something necessary I'm missing here, or is it a bug?