window.setTimeout问题

function admin_login(form){
    if(form.author.value==''){
        form.author.focus();
        $("msg").innerHTML = "\u8bf7输入用户名！";
        return false;
    }
 
    form.logins.disabled = true;
    form.logins.value = "\u6b63在登錄!请稍后...";
     
    // 我要的效果是5秒后才 return true; 现在的效果是直接 return true了
    window.setTimeout("return true;",5000);
    //return true;
}