C# Timer or Thread.Sleep

A timer is a better idea, IMO. That way, if your service is asked to stop, it can respond to that very quickly, and just not call the timer tick handler again... if you're sleeping, the service manager will either have to wait 50 seconds or kill your thread, neither of which is terribly nice.

class Program
{
    static void Main(string[] args)
    {
        Timer timer = new Timer(new TimerCallback(TimeCallBack),null,1000,50000);
        Console.Read();
        timer.Dispose();
    }

    public static void TimeCallBack(object o)
    {
      curMinute = DateTime.Now.Minute;
      if (lastMinute < curMinute) {
       // do your once-per-minute code here
       lastMinute = curMinute;
    }
}

The code could resemble something like the one above

It's important to understand that your code will sleep for 50 seconds between ending one loop, and starting the next...

A timer will call your loop every 50 seconds, which isn't exactly the same.

They're both valid, but a timer is probably what you're looking for here.