  We compute time delays for gravitational lensing in a flat LambdaCDM Swiss
cheese universe. We assume a primary and secondary pair of light rays are
deflected by a single point mass condensation described by a Kottler metric
(Schwarzschild with Lambda) embedded in an otherwise homogeneous cosmology. We
find that the cosmological constant's effect on the difference in arrival times
is non-linear and at most around 0.002% for a large cluster lens; however, we
find differences from time delays predicted by conventional linear lensing
theory that can reach ~4% for these large lenses. The differences in predicted
delay times are due to the failure of conventional lensing to incorporate the
lensing mass into the mean mass density of the universe.
