We have analyzed the influence of the wave packet size in the relativistic tunnelling time τ and its uncertainty τ when it traverses a given potential barrier. The analytical expressions obtained for both magnitudes confirm that the size of the incident pulse has a significant effect on the tunnelling process. This effect is greater for short pulses, compared with the length of the barrier. For the evanescent zone, we have derived an analytical expression for τ with a good limit of validity. This expression constitutes a value tool to calculate the relativistic tunnelling time as a function of the incident wave packet with a good limit of validity. Superluminal propagation is found in this region but with a large value of the uncertainty τ compared with the tunnelling time itself. We can conclude that the probability of superluminal propagation is practically negligible in the evanescent region. In respect to the Klein zone, we have derived an analytical expression for τ that depends on the size of the incident wave packet and the width of the Lorentzian resonance r. This equation fits extremely well with our numerical results for Lorentzian resonances near the top of the Klein zone, where the overlap between them is negligible. As in the evanescent case, superluminal propagation is not likely to occur in the Klein region.