C# adding text every five minutes

You don't need to launch a thread for this purpose. Use the System.Timers.Timer class instead.

Example:

using System;
using System.Timers;

namespace ConsoleApplication4
{
    class Program
    {
        private static Timer m_timer;
        static void Main (string[] args)
        {
            m_timer = new Timer (5 * 1000.0 ); // set timer interval to 5 min.
            m_timer.Elapsed += m_timer_Elapsed;
            m_timer.Start ();

            /* Do other real work here in the meantime
             * --------------------------------------- */

            Console.WriteLine ("Press carriage return to end program.");
            Console.ReadLine ();
        }

        static void m_timer_Elapsed (object sender, ElapsedEventArgs e)
        {
            Console.WriteLine (DateTime.Now.ToString ()); 
        }
    }
}