You want to be watering by your eye as much as anything keep an eye on the soil as Weather can fluctate on how quickly the Plant uses the water. The best time to water is early morning before the sun has a chance to start Heating then dont water again until your plant looks ready sounds weird but you can tell .....
Once every 2 days and due to it being outdoors i would only use 1/2 litre for 3Ft plant.
Like Smoketobehappy said Your plant needs growing and breathing space jsut as much as it needs water.