  Quantum fluctuations of the metric provide a decay mechanism for black holes,
through a transition to a white hole geometry. Old perplexing results by Ambrus
and H\'aj\'i\v{c}ek and more recent results by Barcel\'o, Carballo-Rubio and
Garay, indicate a characteristic time scale of this process that scales
linearly with the mass of the collapsed object. We compute the characteristic
time scales involved in the quantum process using Lorentzian Loop Quantum
Gravity amplitudes, corroborating these results but reinterpreting and
clarifying their physical meaning. We first review and streamline the classical
set up, and distinguish and discuss the different time scales involved. We
conclude that the aforementioned results concern a time scale that is different
from the lifetime, the latter being the much longer time related to the
probability of the process to take place. We recover the exponential scaling of
the lifetime in the mass, a result expected from na\"ive semiclassical
arguments for the probability of a tunneling phenomenon to occur.
