Example Effects Manager in C#

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Timers;

namespace EffectsManager
{
    class Program
    {
        static void Main(string[] args)
        {

            EffectManager em = new EffectManager((change, effect) =>
            {
                Console.WriteLine("Effect: " + effect.ToString() + " is " + change.ToString());
            });
            em.AddEffect(Effect.Type.Slow, 0.05f, 5000L);
            em.AddEffect(Effect.Type.SpeedIncrease, 0.15f, 3000L);

            while (true) {

            }
        }
    }
}

public class Effect
{
    public enum Type
    {
        Slow,
        SpeedIncrease,
        SpeedDecrease,
    }

    public Type type;
    public long until;
    public float strength;

    public Effect(Type type, float strength, long until)
    {
        this.type = type;
        this.strength = strength;
        this.until = until;
    }

}

class EffectManager
{
    public enum EffectChange
    {
        Added, Ended
    }

    Action<EffectChange, Effect.Type> onEffectChange;
    SortedList<long, Effect> queue = new SortedList<long, Effect>();

    public EffectManager(Action<EffectChange, Effect.Type> effectChangeListener)
    {
        onEffectChange = effectChangeListener;
    }

    internal void AddEffect(Effect.Type effect, float strength, long duration)
    {
        long until = DateTimeOffset.Now.ToUnixTimeMilliseconds() + duration;
        queue.Add(until, new Effect(effect, strength, DateTimeOffset.Now.ToUnixTimeMilliseconds() + duration));
        onEffectChange(EffectChange.Added, effect);
        UpdateTimer();
    }


    private void UpdateTimer()
    {
        if (queue.Count == 0)
            return;
           
        Effect next = queue.First().Value;
        if (next != null)
         {
            long interval = next.until - DateTimeOffset.Now.ToUnixTimeMilliseconds();
            System.Timers.Timer timer = new System.Timers.Timer(interval);
            timer.Elapsed += RemoveEffect;
            timer.Enabled = true;
        }

    }

    private void RemoveEffect(Object source, ElapsedEventArgs e)
    {
        if (queue.Count == 0)
            return;
        Effect ended = queue.First().Value;
        queue.RemoveAt(0);
        onEffectChange(EffectChange.Ended, ended.type);
        UpdateTimer();
    }
}