Depending on the particular plant it can take just a few days or as long as a couple of months until the seedling emerges from the seed and builds out the cotyledons. This seed leaves bring sometimes the seed coat above ground and emerge fully only afterwards. Between the cotyledons the first real leaves, called primary leaves, already show. How fast a plant is growing depends on multiple conditions. At first the seedling grows due to the natural nutrients stored in the seed that are being transported to the basic parts of the plant and being used as growing materials. A big seed contains a lot of nutrients and the seedling grows accordingly big right from the start. After the cotyledons are being developed, it is mostly the necessary light for the photosynthesis, the temperature and the watering that determine the further growth. Even if the seedling seems to suddenly stop growing, the plant develops then its roots more intensely to create the base for optimal nutrient supply, which is necessary for your seedlings to growth above ground as well.
The water should be as less lime-deficient as possible. Unfortunately, in most cities the tap water is rather hard and limy. The