It depends on how premature your baby is, and how quickly he/she develops.
Premature babies usually remain in the incubator for about a week.
They are weighed every morning and depending on weight gain they are then placed in an ordinary cot in a neonatal unit (though they are kept apart from others because of the increased risk of infection.)
The baby should be ‘stuffed’( for want of a more elegant turn of phrase!) as much as possible with supplements and milk to boost his/her growth. Usually when the baby weighs 2 kilos you can take him/her home.