Benefits of watering

Here is animation of day-by-day progress made by two seedlings I accidentally put into one cell (just didn't notice first seed when transferred the second one)

See how growth speed increased last 2 days? That's after I really watered them. Apparently, I kept soil too dry by watering it just by condensate from lid couple times a day. This time I watered it generously and going to wait until it dries again.
Also since I installed 24H lighting, plants stopped to grow vertically and instead began to develop leaves very quickly. Some of them already have third pair of leaves, relatively large ones:

The only issue I see is some rocks turning somewhat green:

Hopefully it's something like healthy moss and is not harmful. Obviously, humidity is around 100% in the propagator so something had to grow there apart from seedlings. Can it be sphagnum?
Last couple days two more seeds germinated on filter paper. Since nothing has shown up on sphagnum since week ago nor anything ever germinated on soil, I scrapped these experimental cells and they're going to be used for transferred seedlings.