how do i use timer control with time interval of 2 sec. and 5 sec. alternatively?

System.Timers.Timer tmr = new System.Timers.Timer();
DateTime startTime;

private void Form1_Load(object sender, EventArgs e)
{
    tmr.Interval = 2000;
    tmr.Elapsed += new System.Timers.ElapsedEventHandler(tmr_Elapsed);
    startTime = DateTime.Now;
    tmr.Start();
}

void tmr_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
    if (tmr.Interval == 2000)
        tmr.Interval = 5000;
    else
        tmr.Interval = 2000;

    Console.WriteLine("Elapsed Seconds: " + (DateTime.Now - startTime).TotalSeconds.ToString());

    //Stop the Timer after 10 minutes
    if ((DateTime.Now - startTime).TotalMinutes > 10)
        tmr.Stop();
}