  Relative phases of atomic above-threshold ionization wavepackets have been
investigated in a recent experiment [L. J. Zipp, A. Natan, and P. H. Bucksbaum,
Optica \textbf{1}, 361-364 (2014)] exploiting interferences between different
pathways in a weak probe field at half the frequency of the strong ionization
pulse. In this work we theoretically explore the extraction of phase delays and
time delays of attosecond wavepackets formed in strong-field ionization. We
perform simulations solving the time-dependent Schr\"odinger equation and
compare these results with the strong-field and Coulomb-Volkov approximations.
In order to disentangle short- from long- ranged effects of the atomic
potential we also perform simulations for atomic model potentials featuring a
Yukawa-type short-range potential. We find significant deviations of the
\textit{ab-initio} phase delays between different photoelectron pathways from
the predictions by the strong-field approximation even at energies well above
the ionization threshold. We identify similarities but also profound
differences to the well-known interferometric extraction of phase- and time
delays in one-photon ionization.
