L. the lactation consultant here.
Congratulations on the birth of your baby! Sounds like breastfeeding is going well.
To answer your question, the amount of time it takes to replace a specific volume of milk varies from mother to mother and from feeding to feeding. The breasts constantly produce milk. As milk is removed, more milk is produced - sometimes even on the spot. The speed of production actually increases, depending on how empty the breast is. That's why, especially in the early weeks of breastfeeding, frequent feedings help increase milk supply. Research has shown that babies do not take all the milk available from the breast - the amount that baby drinks depends upon his appetite. The amount of milk removed from the breast varies, but averages around 75-80% of the available milk.
If you're getting too full at night, it's most likely because baby's sleeping longer between night-time feedings, and your breasts are storing milk in preparation for baby's next feeding. Rather than pumping, you might consider just scooping up your sleeping son, nurse him - trust me, a sleeping baby WILL nurse, and your supply issues should resolve.