Even a very slow drip emitter will output at least 1/2 gallon per hour. Two gallons of water will be excessive for most 3 to 5 gallon pots. Slow drip is designed to be slow enough for water-capillary-action to be effective. The absorption of water in a lateral direction. Gravity naturally is responsible for downward direction and a balance between these two forces is what is needed. With good distribution across the surface of your soil, slow drip will be effective this way in as little as 5 minutes, but not as little as 5 to 30 seconds (which is typical with most hand or fast-feed devices).
This is an example of a system which will provide thorough wetting of the soil structure, and maximum root growth.
http://www.youtube.com/watch?v=Ouz-t6bZ8dM
The optimum for the amount of water to apply is achieved when the entire root system is moist and before any significant run-off occurs. Run-off leaches nutrients from the soil.