ZEKE spectroscopy is based on delayed detection by pulsed field ionization. It is thereby possible to monitor the time evolution at a given excitation frequency. Moreover, by varying the depth of detection, one can harvest different Rydberg series. The qualitative features expected for such a spectrum are discussed. The quantitative theory required to compute spectra is outlined and applied to the realistic example of Na2+. The computed spectrum is found to very accurately exhibit two time scales, just as has been observed, with the shorter decay time being faster for lower Rydberg states. Extensive interseries coupling is noted.