I would say that a dummy shouldn't be given regulalry until baby is 8 weeks+. The comfort sucking that most people say is unneccessary is actually still important. Your baby wants to be held as well as to nurse, so to put them down in a moses basket/bouncer chair with a dummy is only fulfilling thier need for oral gratification, not thier need for physical contact and closeness. Also, even comfort sucking delivers some milk to the baby and stimulation to the breasts, which helps baby grow and develop and mums milk supply to be plentiful.
No matter what anyone says there is a lot of research which indicates that dummy use interferes with breastfeeding, can contribute to poor latch and inefficient breastfeeding, which can result in low milk suply and sore nipples. Add to this the alteration of oral/facial bone development that artificial nipples can cause and you have a whole heap of reasons to steer clear of dummies completely, never mind the first few weeks!
Far better to nurse your baby as often as s/he wants, including "comfort" nursing, and carry them in a sling so that they are comforted and pacified without the need for a plastic and silicone boob substitute.