This depends on the age of the baby. The results of a recent study has directed doctors to advise that newborns should only be in a car seat for 20mins. Experts discovered that the combination of a baby’s chin on chest and weak neck muscles, restricted their airway and oxygen supply to the brain starts to lower. In 20 mins the oxygen level drops to unhealthy levels. Once your baby is able to move it’s head and chin this risk drops (usually around one month or two). Pediatricians advise that any head holding device fitted in the car seat needs to be taken out until the baby can lift its chin. Once the baby reaches 2months or more the common advice is up to 1.5hrs.