The spin-orbit autoionization dynamics of a Rydberg electron wave packet in Ar have been investigated using time-dependent multichannel quantum defect theory (TD-MQDT). The time-dependent photoionization cross sections reveal interesting interference patterns in the recurrence spectra which can be accounted for in terms of the quantum defects of the autoionizing channels. An expression for the time-and energy-dependent asymmetry parameter beta(E,t) has been derived to calculate time-resolved photoelectron angular distributions (PADs) for the first time. An oscillation in the time-resolved PAD is observed, with a period which is inversely proportional to the difference between the quantum defects of the autoionizing channels.