C# – Time Elapsed/StopWatch

I want to create an ASP.NET WinForms application that tracks time on task. I need to be able to write the form so that I can add the task to the database, open it in a new tab, and be able to start, pause, and stop the task. When I'm finished, I need to calculate the time taken to complete the task. I would like to have a view of the stopwatch running on the page, showing hours:min:sec updating every second via AJAX. I have already looked on the web at TimeSpan, DateTime, StopWatch, etc. and I can't seem to find anything that works for me. I started with a simple form with start and stop buttons. The _click event for the start button assigns my DateTime variable 'startTime = DateTime.Now' and the _click event for the stop button assigns my DateTime variable 'endTime = DateTime.Now'. I then use a TimeSpan 'elapsed' to calculate TimeSpan 'elapsed = (endTime – startTime). When I update a label to show the time elapsed, I'm expecting to get just the seconds that have gone by, but I get the entire DateTime string. Below is my code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Diagnostics;

namespace CS_StopWatch
{
    public partial class Default : System.Web.UI.Page
    {
        //public Stopwatch myStopWatch = new Stopwatch();
        public DateTime startTime;
        public DateTime endTime;
        public TimeSpan ts_timeElapsed;
        public string s_timeElapsed;
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void StartButton_Click(object sender, EventArgs e)
        {
            //myStopWatch.Start();
            startTime = DateTime.Now;
        }

        protected void StopButton_Click(object sender, EventArgs e)
        {
            //myStopWatch.Stop();
            //ElapsedLabel.Text = "Time Elapsed: " + myStopWatch.Elapsed;
            endTime = DateTime.Now;
            ts_timeElapsed = (endTime - startTime);
            s_timeElapsed = GetElapsedTimeString();
            ElapsedLabel.Text = "Time Elapsed: " + s_timeElapsed;
        }

        public string GetElapsedTimeString()
        {
            int days = ts_timeElapsed.Days;
            double hours = ts_timeElapsed.Hours;
            double mins = ts_timeElapsed.Minutes;
            double secs = ts_timeElapsed.Seconds;
            string x = "";
            if (days != 0)
            {
                x += days.ToString() + ":";
            }
            if (hours != 0)
            {
                x += hours.ToString() + ":";
            }
            if (mins != 0)
            {
                x += mins.ToString() + ":";
            }
            if (secs != 0)
            {
                x += secs.ToString();
            }

            return x;
        }
    }
}