效果截图：

HTML代码：

<span>通话时间： <span id="callTime">00:00:00</span></span>

JS代码：

var secondIndex = 0; // 初始值
var callTimesInter; // 定时器

times = {

    /**
     * 时分秒换算函数
     * @param {Object} value 秒
     */
     formatSeconds: function(value){
        var secondTime = parseInt(value); // 秒
        var minuteTime = 0; // 分
        var hourTime = 0; // 小时
        if(secondTime > 60) {
            minuteTime = parseInt(secondTime / 60);
            secondTime = parseInt(secondTime % 60);
            if(minuteTime > 60) {
                hourTime = parseInt(minuteTime / 60);
                minuteTime = parseInt(minuteTime % 60);
            }
        }
        var secondTimes = (parseInt(secondTime) < 10 ? "0" + parseInt(secondTime) : parseInt(secondTime));
        var result = "00:00:" + secondTimes;
        if(minuteTime > 0){
            var minuteTimes = (parseInt(minuteTime) < 10 ? "0" + parseInt(minuteTime) : parseInt(minuteTime));
            result = "00:" + minuteTimes + ":" + secondTimes;
        }
        if(hourTime > 0){
            var hourTimes = (parseInt(hourTime) < 10 ? "0" + parseInt(hourTime) : parseInt(hourTime));
            result = hourTimes + ":" + minuteTimes + ":" + secondTimes;
        }
        return result;
    },
    
    // 通话时间初始化
    callTimeLoad: function(flag){
        if(flag){
            callTimesInter = setInterval(function(){
                secondIndex++;
                let time = times.formatSeconds(secondIndex);
                $("#callTime").text(time);
            }, 1000);
        }else{
            clearInterval(callTimesInter);
            secondIndex = 1;
        }
    },
    
}

函数调用：

times.callTimeLoad(true); // 开始时间计算
times.callTimeLoad(false); // 结束时间计算