The seedlings are still in infancy. The stems are still white when they should already be turning green. When that happens the root system will take off. So maybe another week or 2 before roots come out of the cubes.
I would add the slightest amount of fertilizer to the water now it will quicken the process. Increase
nutrient watering once every 2 hours during daylight hours the seedling will suck up all the
nutrients they need to grow faster.