  We study propagation effects due to the finite speed of light in ionization
of extended systems. We present a general quantitative theory of these effects
and show under which conditions such effects should appear. The finite speed of
light propagation effects are encoded in the non-dipole terms of the
time-dependent Shr\"odinger equation and display themselves in the
photoelectron momentum distribution projected on the molecular axis. Our
numerical modeling for the \Hp molecular ion and the \Ne dimer shows that the
finite light propagation time from one atomic center to another can be
accurately determined in a table top laser experiment which is much more
readily affordable than an earlier synchrotron measurement by Grundmann {\em et
al} [Science 370, 339 (2020)]
