You are right... I failed to properly cover this phase. Here is something I have been working on, and lets add it now to this thread as:
The Seedling Watering Addendum:
When starting a seed in a solo cup it is important at first to keep the seed wet, until it gathers enough energy to send the seedling up to the surface. I water with just a small amount, or spray, twice a day until I see the new green plant surface.
By this time the soil in the entire cup should be fairly wet from the twice daily sprayings. Stop watering twice a day and until the second set of leaves come out, continue to water once a day with just a tiny amount, right down the center, so that the water as it falls to the bottom because of gravity, shows the new tap root how to find the bottom.
The second set of leaves coming out is time to start weaning the plant from all this water by forcing it to start using the water already in the soil. The plants will not have established a good root base yet and when you water they will tend to float around. As long as you can see that the plant is still not yet stable, continue to spray or very lightly water when it is time once a day. Once the plant stabilizes in position make the plant wait a full day between waterings and watch those new leaves get bigger by the day. After a couple of waterings the plant will start showing that it is steady and fixed, we call it "established", and then instead of watering around the middle of the plant, extend a circle out to 3x the diameter of the plant. Every three days, if the plant has not yet drained all of the water from the cup, lightly water the outside edge of this circle 3x the diameter of the plants, enticing the roots to grow out that direction. Every 3 days repeat this and in-between those waterings, let the plant work on using all of the water in that cup.
Soon, 3x the diameter of the plant will hit the edges of the container. This is your signal to start properly watering. Water lightly around that outside edge every 3 days, unless the plant has managed to use all of the water in the cup. You can tell when this happens because when you lift the cup up, it will be as light as a feather and you will not be able to tell by weight that there is any water in there at all. Until this happens, continue to water lightly around the edge every 3 days, giving only enough water to go down 3 or 4 inches deep.
Once the plant finally uses all of the water in the bottom of the cup, slowly water the container to saturation (runoff), or by slowly trying to get the cup to hold the most amount of water possible, until any added after that simply comes out of the bottom as runoff. Treat that soil as if it was a sponge, and you are trying to get every last drop in there that it will hold.
Then, do nothing for at least 3 days. If the plant has not drained all the water by then to the light as a feather status, simply water lightly around the edges to 3-4 inches deep and wait another day. Check each day until it is time to water.
Repeat this wet/dry cycle over and over. Each time you do, the time between waterings will get shorter and shorter. Eventually the roots in that cup will be so strong that the plant will be able to use every bit of water you could get in there, in 24-36 hours. When the plant can do this the first time, it is time to uppot to at least a 3x bigger container, and start this wet/dry cycle process all over again.