What soil are you starting with? Typically pre-mixed soils will have some nutrients in them, this can carry you through your first 2-6 weeks (or more if also supplementing with teas). This will also vary depending on the strain and frequency of waterings. If you flush often, you may find you need more nutrients added to your medium.
Many people i soil will increase their pot size a couple times during veg, this will also give you a boost in nutrients available making feeding almost unnecessary until you are in flower.