  A unified approach to the time analysis of tunnelling of nonrelativistic
particles is presented, in which Time is regarded as a quantum-mechanical
observable, canonically conjugated to Energy. The validity of the Hartman
effect (independence of the Tunnelling Time of the opaque barrier width, with
Superluminal group velocities as a consequence) is verified for ALL the known
expressions of the mean tunnelling time. Moreover, the analogy between particle
and photon tunnelling is suitably exploited. On the basis of such an analogy,
an explanation of some recent microwave and optics experimental results on
tunnelling times is proposed. Attention is devoted to some aspects of the
causality problem for particle and photon tunnelling.
