[jQuery] clueTip: openSpeed argument?

The API is a little lacking so I was wondering if somone could tell me
what the accepted values can be for this argument to clueTip. I want
the clueTip to show up instantly, not fast. Instantly! Is there a way?
$('a.preview').cluetip({
    splitTitle: '|',
    fx: {
        open: 'show', // can be 'show' or 'slideDown' or 'fadeIn'
        openSpeed: 'fast'
    }
});