RunStopwatch.cs

static void Main(string[] args)
{
    RunStopwatch(() =>
    {
        foreach (var item in collection)
        {
            DoSomething(item);
        }
    });
}


public static void RunStopwatch(Action action)
{
    // Run action, record timespan

    Stopwatch stopwatch = new Stopwatch();

    stopwatch.Start();

    action();

    stopwatch.Stop();

    Console.WriteLine(stopwatch.ElapsedMilliseconds);
}