  The explicit form for the post-Newtonian gravitational time delay of light
signals propagating on the equatorial plane of a Kerr-Newman black hole is
derived. Based on the null geodesic in Kerr-Newman spacetime, we adopt the
iterative method to calculate the time delay. Our result reduces to the
previous formulation for Kerr black hole if we drop off the contribution from
the electrical charge. Our time-delay formula for the Reissner-Nordstr\"{o}m
geometry is different from the previous publication [Phys. Rev. D 69, 023002
(2004)], in which the largest second-order contribution to the time delay is
missing.
