var d=Math.floor(t/1000/60/60/24);
       var h=Math.floor(t/1000/60/60%24);
       var m=Math.floor(t/1000/60%60);
       var s=Math.floor(t/1000%60);

       document.getElementById("t_d").innerHTML = d + "天";
       document.getElementById("t_h").innerHTML = h + "时";
       document.getElementById("t_m").innerHTML = m + "分";
       document.getElementById("t_s").innerHTML = s + "秒";

时间的计算