I added nutrients at about 1 week and 1/2. I add nutes every other feeding. No, don't water your plant if the root doesn't touch, if you are using the AG sponges, they will suck up water to the root, I never water them manually. Just let the AG do its thing.
Even though I added nutes after a week, I heard that you should always used nutes, even if its a tiny amount. I used 4ml of that starter nutes that come with the AG seed kits, and it didn't seem to hurt them at all. I use that to get them used to nutes, then I add my other grow nutes (Floranova Grow)