Timer triggers some action every 500ms and can be stopped or started with button press.

TimerPeriodic.cs

namespace TimerElapsed
{
    using System;
    using System.Timers;

    public class Program
    {
        static Timer myTimer;

        static void Main(string[] args)
        {
            myTimer = new Timer();
            myTimer.Elapsed += OnMyTimerElapsed;
            myTimer.Interval = 500;
            myTimer.AutoReset = true;
            myTimer.Enabled = false;

            Console.WriteLine("\nStart(): {0}", DateTime.Now);

            Console.WriteLine("Usage:\n" +
                "a: start timer\n" +
                "b: stop timer\n" +
                "c: print current timer state (enabled, elapsed)\n" +
                "ESC, Ctrl+C to exit\n");

            ConsoleKeyInfo keyinfo;
            do
            {
                keyinfo = Console.ReadKey();

                if (keyinfo.Key == ConsoleKey.A)
                {
                    Console.WriteLine($"\nEnable and start timer {DateTime.Now}");
                    myTimer.Enabled = true;
                    myTimer.Start();
                }

                if (keyinfo.Key == ConsoleKey.B)
                {
                    Console.WriteLine($"\nDisable and stop timer {DateTime.Now}");
                    myTimer.Enabled = false;
                    myTimer.Stop();
                }

                if (keyinfo.Key == ConsoleKey.C)
                {
                    Console.WriteLine($"\ntimer status: enabled={myTimer.Enabled}");
                }
            }
            while (keyinfo.Key != ConsoleKey.Escape);
        }

        private static void OnMyTimerElapsed(object source, ElapsedEventArgs e)
        {
            Console.ForegroundColor = ConsoleColor.DarkYellow;
            Console.WriteLine($"\nelapsed {DateTime.Now}");
            Console.ResetColor();
        }
    }
}