Water Runoff When?

Every time you water. It is the only way to know that water has reached the bottom of the pot, the exact place where most of the roots are located. Deep watering every few days to run off is much, much better than giving small amounts of water trequently. And water the entire pot, from edge to edge and not just near the stem, which just encourages shallow roots. Wait until the top 2cm or so are dry before watering again, there is no need to water every day or every 2 days "just because", water only once the top inch or so has dried out from the previous watering. Watering to run off helps prevent nutrient salts from building up to toxic levels in the substrate and then causing burning or other damage. You could also add some more potting mix, ideally the peat plug should be below the surface of the soil in the pot. It is perfectly ok to bury some of the stem, in time it will sprout roots and help your plant grow. Hope this helps, Organoman.

Speaking off experience I just gained earlier this year. I would considering watering up until runoff anytime past week 2/3 of veg. Although watering seedlings may look beneficial, less is always more. Once a great grower told me: it is always easier to increase whenever not enough, but once you overwater/overfeed your plant it is going to get stunted, and you must deal with it. If your solution is rather light and manageable, there should be no issues in salt buildups up until week 3/4. Then I just start watering with a 20% runoff everyday (mind that I am talking bout coco as growing medium). I also schedule a weekly flush with phwater just to keep the football ppm low and in check.