  We investigate attosecond time delays in the emission of photoelectrons using
a hierarchy of models of the $CO_2$ molecule including the strong field
approximation, Coulomb-scattering, short-range parts of the molecular
potential, Hartree and Hartree-Fock descriptions. In addition, we present an
{\it ab initio} calculation based on quantum-chemical structure in combination
with strong-field techniques, which fully includes multi-electron exchange and
correlation. Every single of these model constituents is found to modify delays
on the scale of 10 as or more, with exchange and correlation having the most
pronounced effect.
