ReactiveScheduler

Program.cs

namespace Scheduler
{
    class Program
    {
        static void Main(string[] args)
        {
            Scheduling.ScheduleWithEnd();
            Scheduling.ScheduleWithoutEnd();

            Console.ReadKey();
        }  
    }
}

Scheduling.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reactive.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Scheduler
{
    static class Scheduling
    {
        static void ScheduleWithEnd()
        {
            Observable.Defer(() =>
            DateTime.Now.Hour < 19
              ? Observable.Timer(DateTime.Today.AddHours(9))
              : DateTime.Now.Hour < 13
              ? Observable.Timer(DateTime.Today.AddHours(13))
              : Observable.Timer(DateTime.Today.AddDays(1).AddHours(9)))
          .Repeat(10)
          .Subscribe(id => { Console.WriteLine("Hi" + System.Threading.Thread.CurrentThread.ManagedThreadId); });
        }

        static void ScheduleWithoutEnd()
        {
            var clock = from _ in Observable.Interval(TimeSpan.FromSeconds(1))
                        select DateTime.Now;

            clock.Subscribe(now =>
            {
                Console.WriteLine("It's now {0} o'clock", now);
            });
        }
    }
}