How do I display timer in textbox?

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C#

Hello,

I am new to C#,i have few doubts regarding the MVVM. When to use the IVauleConverter and the binding concept? To understand the concept,I have written a small demo project.
Actually I am trying to implement the small project where i have first name ,last name,full name, timer and ellipse.The timer text box has to display the time when ever the time handler event arises and the color of ellipse has to change. I want to write code for ui separately and logic must be different.In the below code,Its not displaying the time in timer text box.

What I have tried:

private DispatcherTimer atimer;
        public Person personobj { get; set; }

       public MainWindow()
        {
            InitializeComponent();
            personobj = new Person();
            personobj.firstName = "hello";
            personobj.lastName= "";
           
            this.DataContext = personobj;
            // aTimer = new System.Timers.Timer(2000);
            // aTimer.Elapsed += new ElapsedEventHandler(OnTimeEvent);
            // aTimer.Enabled = true;
         //   atimer = new DispatcherTimer();
           // atimer.Interval = TimeSpan.FromMilliseconds(5000);
            //atimer.Tick += new EventHandler(OnTimeEvent);
            //atimer.Start();

        }

        /*private void OnTimeEvent(object sender, EventArgs e)
        {
            //TimerCount.Text = DateTime.Now.ToString("hh:mm:ss");
           // throw new NotImplementedException();
        }*/
    }

    public class Person : INotifyPropertyChanged
    {
        
        /// <summary>
        /// 
        /// 
        public String firstName;
        public String lastName;
        public String fullName="";
        private Boolean colorchange=false;
        private String timeIndicator;
        private DispatcherTimer timeCount;
        public Person()
        {
            timeCount = new DispatcherTimer();
            timeCount.Tick += new EventHandler(Timer_Tick);
            timeCount.Interval = TimeSpan.FromMilliseconds(5000);
            timeCount.Start();

        }
        public String FirstName
        {
            get
            {
                return firstName;
            }

            set
            {
                if (firstName != value)
                {
                    firstName = value;
                    OnPropertyChanged("FirstName");
                    OnPropertyChanged("FullName");
                }
            }
        }

        public String LastName
        {
            get
            {
                return lastName;
            }

            set
            {
                if (lastName != value)
                {
                    lastName = value;
                    OnPropertyChanged("LastName");
                    OnPropertyChanged("FullName");
                }
            }
        }

        public String FullName
        {
            get
            {
                //  Debug.WriteLine(fullName);
                return this.fullName = firstName + " " + lastName;

            }

            set
            {
                this.fullName = value;
                OnPropertyChanged("FullName");
                /*if (fullName != "")
                  {
                      colorchange = false;
                  }
                  else
                  {
                      colorchange = true;
                  }*/



                  }
            }


        public Boolean Colorchange
        {
            get
            {
                return colorchange;
            }

            set
            {
                colorchange = value;
                OnPropertyChanged("Colorchange");
            }
        }

        public string TimeIndicator
        {
            get
            {
                return timeIndicator;
            }

            set
            { 
                timeIndicator = value;
               if (timeIndicator != null)
                  {
                      colorchange = true;
                  }
                  else
                  {
                      colorchange = false;
                  }

                OnPropertyChanged("TimeIndicator");
            }
        }
      

        private void Timer_Tick(object sender, EventArgs e)
        {
            TimeIndicator = DateTime.UtcNow.ToString("hh:mm:ss");
        //    OnPropertyChanged("TimeIndicator");
        }
      //  public delegate PropertyChangedEventHandler(string property);
        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string property)
        {
            if (PropertyChanged != null)
            {
                 PropertyChanged(this, new PropertyChangedEventArgs(property));
        //        PropertyChanged(property);
            }
        }


    }
   // [ValueConversion(typeof(Person), typeof(Brush))]
    public class ColorChange : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
         //  Boolean BooleanValue = (Boolean)value;
         
            if (value.ToString()!= null)
            {

                return value.ToString();

            }
            else
            {
                return (object)Brushes.Green;
            }
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
           if (value is bool)
            {
                if ((bool)value == true)
                    return new SolidColorBrush(Colors.Green);
                else
                    return new SolidColorBrush(Colors.Red);
            }
            return null;
        }
    }
}

<window.resources>
        <local:ColorChange x:Key="ColorChange"/>
    
    <grid>
        
        <TextBox  Text="{Binding Path=FirstName, Mode=TwoWay}" Margin="145,20,187,264" />

        
        <TextBox  Text="{Binding  Path=LastName, Mode=TwoWay}" Margin="145,75,187,209" />
        
        <TextBox Name="fulltxtname" Text="{Binding Path=FullName, Mode=TwoWay}"  Margin="145,125,187,159"/>
      
        
        <TextBox Name ="TimerCount" Text="{Binding Path=timeIndicator,Mode=TwoWay }" Margin="75,200,297,89"/>
        <Ellipse Fill="{Binding ElementName=TimerCount, Converter={StaticResource ColorChange}}" HorizontalAlignment="Left" Height="35" Margin="260,195,0,0" Stroke="Black" VerticalAlignment="Top" Width="40"/>