The plants should be watered once a day. This is usually best at the first of the morning, but they can be watered any time.
The nutrient water is dipped into the watering can and then poured over into the plant grower. It is poured until excess water starts coming out the drain hole.
When seedlings are very young, their stems are usually weak and water should either be poured around the plants or gently poured over the leaves. This can be accomplished by holding your hand between the poring water and the plants below, to soften the force of the water.
It usually helps plant growth to receive nutrient water over their leaves, especially young seedlings. This can be tested in an experiment.
If the drainhole is in the grower, you cannot pour too much water as all the excess will just continue to drain. As you get experienced, you will have a feel for how much water is required each day. This should be more on sunny days than cloudy days.
The plant can usually go for two days without watering, so they do not need to be watered over a weekend. The plant conserves water by shutting its pours when it does not see water available. In addition, the water reservoir should contain enough water for a day or two.
Letting the plant go longer, a week for example will probably cause a problem. You usually can see this is wilting and drying. If caught soon enough it may be possible to save the plant.
Revised: 1 May 2016