There is no fixed number of sittings . If your baby has regained to its birthweight then feed on demand whether she needs every hour or every 3 hours. Again there is no minimum duration but if she is falling asleep within few mins of feeding; then tickle her ears or tap her feet to wake her up.if baby demands feed after every nature's call, yes please feed her. Newborn tummies r very small & breast milk being fully digestible digests soon.