I've set the time to 1000*36000.
function display() {
var now = new Date();
var time = now.getTime();
var expireTime = time + 1000*36000;
now.setTime(expireTime);
document.cookie = 'cookie=ok;expires='+now.toUTCString()+';path=/';
//console.log(document.cookie); // 'Wed, 31 Oct 2012 08:50:17 UTC'
}