  Attosecond photoionisation time delays reveal information about the potential
energy landscape an outgoing electron wavepacket probes upon ionisation. In
this study we experimentally quantify, for the first time, the dependence of
the time delay on the angular momentum of the liberated photoelectrons. For
this purpose, electron quantum-path interference spectra have been resolved in
energy and angle using a two-color attosecond pump-probe photoionisation
experiment in helium. A fitting procedure of the angle-dependent interference
pattern allows us to disentangle the relative phase of all four quantum
pathways that are known to contribute to the final photoelectron signal. In
particular, we resolve the dependence on the angular momentum of the delay of
one-photon transitions between continuum states, which is an essential and
universal contribution to the total photoionization delay observed in
attosecond pump-probe measurements. For such continuum-continuum transitions,
we measure a delay between outgoing s- and d-electrons as large as 12 as close
to the ionisation threshold in helium. Both single-active-electron and
first-principles ab initio simulations confirm this observation for helium and
hydrogen, demonstrating the universality of the observed delays.
