There is no set amount of time for a premature baby to stay in an incubator. Hospitals place most very premature babies or sick babies on open warming beds shortly after birth, so that it is easier to assess them and work on them. Once the baby needs fewer interventions, he generally goes into an incubator, which is an enclosed space that keeps him warm. Once he can maintain his temperature, he will go into an open crib -- the final step before coming home. How long the process takes depends on your baby.

Temperature Stability
The key to making the move from incubator to open crib is your baby's ability to maintain his temperature on his own in room air. Because premature babies do not have as much brown adipose tissue, a type of baby fat or as much subcutaneous fat as full-term babies do, they have more difficulty maintaining their temperature without a heated environment. Premature infants also experience insensible water loss from their increased surface area; keeping them in an incubator reduces fluid loss.
Weight
Your baby's weight helps determine when he is ready to try a move to an open crib. Many hospitals consider that a baby is able to try an open crib once he reaches 1,700 to 1,800 grams, or between 3 pounds, 12 ounces to 3 pounds, 15 ounces, according to an Australian study published in the 2011 "Cochrane Neonatal Reviews." After a review of available studies, the researchers concluded that hospital staff can safely move premature infants to an open crib when they weigh at 1,600 grams, or 3 pounds, 8 ounces -- or possibly, even less.
Gestational Age
Babies start to produce brown adipose tissue, or BAT, between the gestational age of 26 to 30 weeks, according to Birth.com. By 40 weeks, healthy newborns have enough BAT to maintain their temperatures in normal indoor temperatures without difficulty. Sometime between these two points, your baby will be ready for an open crib, but his current weight and medical conditions will determine when he is ready.
Other Factors
Infections, illness and stress can affect your preemie's ability to maintain his temperature adequately. Because of this, he might need to remain in an Cheap Isolettes even though he weighs as much as a normal full-term baby. A baby who cannot maintain his temperature might not gain weight as well as a baby kept in an incubator, because he uses up additional energy keeping his temperature stable.