The length of a time that a turtle can hold its breath underwater depends on the type of turtle and its current level of physical activity. During periods of activity, pet turtles can generally hold their breath for a few minutes to half an hour.
According to the Sea Turtle Conservancy, sea turtles can hold their breath for much longer periods of time. A sea turtle that is not engaged in strenuous activity is able to hold its breath underwater for anywhere from 4 to 7 hours. However, when a sea turtle is hibernating, it may stay underwater for several months at a time. Turtles are able to stay underwater for long periods because of their ability to metabolize oxygen at a very low rate.