This is a myth. Your breasts will never be fully empty. As your baby nurses – or even as you pump – fresh milk is constantly being produced.
Follow your baby’s cues for feeding – as often as your baby shows hunger signs, put her to the breast, and allow her to nurse as long as she wants to on one side, then offer the other breast. If she’s still hungry, she will nurse longer. If not, you may need to pump the unused side to keep from getting overly full, then start on that side at the next feeding.
An average feeding is about 15 minutes per side, but some babies are very efficient and get what they need quickly, while others like to linger over their meals. And just like us, sometimes babies may want a quick snack, and other times they want a big meal.