在Tool bar上面找到

Rules->CustomRules

在class Handlers{ 裡面新增

function BeginRequestTime(oS: Session)
    {
        if (oS.Timers != null)
        {
            return oS.Timers.ClientBeginRequest.ToString();     
        }
        return String.Empty;
    }

    public static BindUIColumn("Time Taken"
 
)
    function CalcTimingCol(oS: Session){
        var sResult = String.Empty;
        if ((oS.Timers.ServerDoneResponse > oS.Timers.ClientDoneRequest))
        {
            sResult = (oS.Timers.ServerDoneResponse - oS.Timers.ClientDoneRequest).ToString();
        }
        return sResult;
    }
 

儲存即可，注意退出fiddler後再儲存。
如圖: