code: function Timer (callback, start) {
    this.callback = callback;
    this.startDate = null;
    if (!exists(start) || start !== false) {
      this.start();
    }
  }
docs: Timer class for performing time calculations through the monitor
  module.
  @class
  @param {function} callback Callback to execute when the timer is stopped.
  @param {boolean} start Whether or not to start the timer upon construction,
  default: `true`.