Stopwatch.cs

// Stopwatch.cs
using System;

namespace Methods
{
    public class Stopwatch
    {
        private TimeSpan _initialTime;
        private TimeSpan _stopTime;
        private bool _hasBeenClicked;

        public void Start()
        {
            if (_hasBeenClicked)
            {
                throw new System.InvalidOperationException();
            }
            
            _hasBeenClicked = true;
            
            _initialTime = DateTime.Now.TimeOfDay;
        }

        public TimeSpan Stop()
        {
            _stopTime = DateTime.Now.TimeOfDay;
            var spanTime = _stopTime.Subtract(_initialTime);
            
            _hasBeenClicked = false;
            
            return spanTime;
        }
    }
}


// Program.cs
using System;
using System.Threading;

namespace Methods
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                var watch = new Stopwatch();

                watch.Start();
                var firsTimeSpan = watch.Stop();
                Console.WriteLine("first timespan: {0}", firsTimeSpan); // first timespan: 00:00:00.0316230

            
                watch.Start();
                Thread.Sleep(1000);
                var secondTimeSpan = watch.Stop();
                Console.WriteLine("second timespan: {0}", secondTimeSpan); // second timespan: 00:00:01.0052090
    
                watch.Start();
                Thread.Sleep(3000);
                var thirdTmeSpan = watch.Stop();
                Console.WriteLine("third timespan: {0}", thirdTmeSpan); // third timespan: 00:00:03.0009240
            
                watch.Start();
                Thread.Sleep(1000);
                var fourthTmeSpan = watch.Stop();
                Console.WriteLine("fourth timespan: {0}", fourthTmeSpan);
                
                watch.Start();
                var fifthTimeSpan = watch.Stop();
                Console.WriteLine("fifth timespan: {0}", fifthTimeSpan); // first timespan: 00:00:00.0000020
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
                throw;
            }
           
        }
    }
}