4 different timer implementations in typescript

timers.ts

module Utilities {
    export class Timer implements eg.IUpdateable {
        private OnTick: eg.EventHandler;
        private _start: number;
        private _interval: number;
        private _started: boolean;
        private _lastTime: number;

        constructor(interval: eg.TimeSpan);
        constructor(interval: eg.TimeSpan, callback?: Function);
        constructor(start: eg.TimeSpan, interval?: eg.TimeSpan);
        constructor(start: eg.TimeSpan, interval?: any, callback?: Function) {
            this.OnTick = new eg.EventHandler();

            this._start = start.Milliseconds;

            if (interval instanceof eg.TimeSpan) {
                this._interval = interval.Milliseconds;
            } else if (interval instanceof Function) {
                callback = <Function>interval;
            } else {
                this._interval = start.Milliseconds;
            }

            if (callback) {
                this.OnTick.Bind(callback);
            }
            
            this._lastTime = new eg.GameTime().Total.Milliseconds;
        }

        public Start(): void {
            this._started = true;
        }

        private Tick(): void {
            this.OnTick.Trigger();

            this._lastTime += this._interval;
        }

        public Stop(): void {
            this._started = false;
        }

        public Update(gameTime: eg.GameTime): void {
            if (this._started && this._lastTime < gameTime.Total.Milliseconds) {
                this.Tick();
            }
        }
    }
}