How to change the default timeout?

Ultrasonic ultrasonic(9, 8); // Trig PIN, Echo PIN

Ultrasonic ultrasonic(9, 8, 17400); // Trig PIN, Echo PIN, Max.TimeOut in µsec

One 1 cm are about ≈ 29 µsec * 2 (away and back) by a default temperature at 22 °C