I've been adding a measured amount of water about every four days. I use a scale to weigh the plants and the amount of water added. By looking at the soil and holding the plant, I've judged that 32 ounces is their ideal weight. Each time I add enough water to bring them back to their "ideal" weight.
I lift the upper (planter) section from the bottom (reservoir) section to add water. It then rises by capillary action through the neck of the bottle which acts as a wick. In my opinion, this is the best way to learn how sub-irrigation (aka "self-watering") works. Unlike opaque grow pots, you can see everything.
You can see the progress of these plant from the time of seed propagation on this Flickr set. It is viewable as a slide show.