<a class="btn btn-default" onclick="StartExamine();">开始</a> 
<div id="TimeClock" class="col-md-4" ><span class="text-danger hour">00</span> <span class="text-danger minute">00</span> <span class="text-danger seconds">00</span></div>

 var gEaminePapeId = 'dfdfad33434342';
    var gExaminePapeTime = '100';    
    var gHour = gExaminePapeTime / 60;    
    var gMinute = gExaminePapeTime % 60; 
    var gSeconds = gExaminePapeTime * 60;
    var hour_elem = $("#TimeClock").find('.hour');
    var minute_elem = $("#TimeClock").find('.minute');
    var second_elem = $("#TimeClock").find('.seconds');
    function StartExamine() { 
      //开始计时      
      var timeClik = setInterval('ShowClock()', 1000);
   }
   function ShowClock() {    
     if (gSeconds > 1) {
       gSeconds -= 1;
       var hour = Math.floor((gSeconds / 3600) % 24);
       var minute = Math.floor((gSeconds / 60) % 60);
       var second = Math.floor(gSeconds % 60);
       $(hour_elem).text(hour < 10 "0" + hour+":" : hour+":"); //计算小时
       $(minute_elem).text(minute < 10 "0" + minute+":" : minute+":"); //计算分钟
       $(second_elem).text(second < 10 "0" + second : second); //计算秒杀
     }
     else {
       clearInterval(timeClik);
       //做题时间到
        ForceSubmit();
     }
   }   
    function ForceSubmit() {
      //强制提交答题
  }