Final answer:
If a newborn does not begin breathing after delivery, resuscitation efforts should be started within 10 seconds.
Step-by-step explanation:
The correct time to begin resuscitation efforts if the infant does not begin breathing after delivery is within 10 seconds. This is because the first breath typically is taken within 10 seconds of birth, after mucus is aspirated from the infant's mouth and nose. The first breaths inflate the lungs to nearly full capacity and dramatically decrease lung pressure and resistance to blood flow, causing a major circulatory reconfiguration.