  Against the background of recent attoclock experiments, the problem of time
delay in tunneling ionization is revisited. The origin of time delay at the
tunnel exit is analysed, underlining the two faces of the concept of the
tunnelling time delay: the time delay around the tunnel exit and the asymptotic
time delay at a detector. We show that the former time delay, in the sense of a
delay in the peak of the wavefunction, exists as a matter of principle and
arises due to the sub-barrier interference of the reflected and transmitted
components of the tunneling electronic wavepacket. We exemplify this by
describing the tunnelling ionization of an electron bound by a short-range
potential within the strong field approximation in a "deep tunnelling" regime.
If sub-barrier reflections are extracted from this wavefunction, then the time
delay of the peak is shown to vanish. Thus, we assert that the disturbance of
the tunnelling wavepacket by the reflection from the surface of the barrier
causes a time delay in the neighbourhood of the tunnel exit.
