Chronos' Timer enables your horses to make progress twice as fast, and therefore complete their training a a young age. Riding, training and learning through competitions are the activities affected by Chronos' Timer.
Be aware that Chronos' Timer will not double the skills your horse can acquire. It will only enable its learning speed to double.
When used with Water Of Youth, Chronos' Timer will still work, but is effectively cancelled out. It will take the same amount of effort to produce the same results, but the horse will only be half the age.
This item cost 2 passes in the Black Market.