I can tell you with 100% confidence that a 1 week old seedling doesnt need watering until runoff. The answer to this question will depend on the style of growing you're doing. Example: If using organic living soil the goal is to keep the soil moist, never bone dry and not soggy. A good rule of thumb when growing like this is 10% water per total vol of soil. So 10 gals of soil is equal to 1 gal of water. That is the ideal moisture level for organic living soil growing. NOW with synthetic or bottled nutrients, run off IS necessary to avoid toxicity of specific micro/macro nutrients. This growing style will require that you measure the runoff PH, PPM, ect ect to make sure you're within limits. It is a more intense style of growing. Regardless, when watering, its important to have your RH set to appropriate levels for the stage of growth. Without the proper RH, your watering frequency and amounts will change. I hope this helps :)