Breast feeding is enough and is also very recommended.
It is rich in nutriments and antibodies.
It is very good both for the mother and the baby.
The average time for suckling is 15 min and it should be repeated as much as the baby requires ( which is every 2-3hours)
The best way to make sure your baby is taking enough is to check the growth curve. ( with the exception of the weight loss within one week of the delivery).