simpler.cs

using System;
using System.Collections.Generic;
using System.Threading;

namespace TimersAreWeird
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var timers = new List<Timer>();

            while (true)
            {
                Console.Write("Waiting for input: ");
                var c = Console.ReadKey();
                Console.WriteLine();
                if (c.Key == ConsoleKey.G)
                {
                    Console.WriteLine("Collecting garbage");
                    GC.Collect();
                }
                else if (c.Key == ConsoleKey.H)
                {
                    Console.WriteLine("Collecting garbage for gen 2 and waiting for finalizers");
                    GC.Collect(GC.MaxGeneration);
                    GC.WaitForPendingFinalizers();
                }
                else if (c.Key == ConsoleKey.D)
                {
                    lock (timers)
                    {
                        Console.WriteLine(timers.Count);
                    }
                }
                else if (c.Key == ConsoleKey.F5)
                {
                    Console.WriteLine("Refreshing");
                    Timer timer = null;
                    timer = new Timer(state =>
                    {
                        timer.Dispose();
                        lock (timers)
                        {
                            timers.Remove(timer);
                        }
                    },
                    null, 1000, Timeout.Infinite);
                    lock (timers)
                    {
                        timers.Add(timer);
                    }
                }
            }
        }
    }
}

timers_are_weird.cs

using System;
using System.Collections.Generic;
using System.Threading;

namespace TimersAreWeird
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var refs = new ExpiredReferencesManager();

            while (true)
            {
                Console.Write("Waiting for input: ");
                var c = Console.ReadKey();
                Console.WriteLine();
                if (c.Key == ConsoleKey.G)
                {
                    Console.WriteLine("Collecting garbage");
                    GC.Collect();
                }
                else if (c.Key == ConsoleKey.H)
                {
                    Console.WriteLine("Collecting garbage for gen 2 and waiting for finalizers");
                    GC.Collect(GC.MaxGeneration);
                    GC.WaitForPendingFinalizers();
                }
                else if (c.Key == ConsoleKey.D)
                {
                    refs.Dump();
                }
                else if (c.Key == ConsoleKey.F5)
                {
                    Console.WriteLine("Refreshing");
                    ThreadPool.QueueUserWorkItem(state =>
                    {
                        var manager = (ExpiredReferencesManager)state;
                        manager.Make();
                    },
                    refs);
                }
            }
        }
    }
    
    public class Expired
    {
        private Timer _timer;
        private Action<Expired> _expiredCallback;
        private static readonly TimerCallback _timerCallback = OnExpired;
        public object Item { get; private set; }

        public Expired(object thing)
        {
            Item = thing;
        }

        public void StartTimer(Action<Expired> callback)
        {
            _expiredCallback = callback;
            _timer = new Timer(_timerCallback, this, 1000, Timeout.Infinite);
        }

        private static void OnExpired(object state)
        {
            var expired = (Expired)state;

            expired._timer.Dispose();
            expired._timer = null;

            var callback = expired._expiredCallback;
            expired._expiredCallback = null;

            callback(expired);

            expired.Item = null;
        }
    }

    public class ExpiredReferencesManager
    {
        private readonly List<WeakReference> _expiredItems = new List<WeakReference>();

        public object Make()
        {
            var obj = new Expired(new object());

            obj.StartTimer(OnExpired);

            return obj.Item;
        }

        private void OnExpired(Expired obj)
        {
            lock (_expiredItems)
            {
                _expiredItems.Add(new WeakReference(obj.Item));
            }
        }

        internal void Dump()
        {
            lock (_expiredItems)
            {
                foreach (var item in _expiredItems)
                {
                    Console.WriteLine(item.IsAlive);
                }
            }
        }
    }
}