The time taken for a star to exhaust its supply of a particular nuclear fuel. The nuclear time-scale may be very short, as with the oxygen-burning phase of some massive stars, which can be less than a year, or very long, as with the hydrogen-burning phase of low-mass stars, which is potentially longer than the age of the Universe. The nuclear time-scale for hydrogen burning in the Sun is about 7 billion years, but becomes shorter with increasing stellar mass because the larger amount of fuel in massive stars is more than offset by the faster rate of burning.