The VASCO project has identified over 100,000 sub-second optical transients on photographic plates from the First Palomar Observatory Sky Survey (1949-1957), all predating artificial satellites. A companion analysis (submitted) established that transient detection rates are dose-dependently suppressed during geomagnetic storms (Z = −3.391, p = 0.0007), ruling out emulsion defects and confirming the transients as real, magnetospherically coupled phenomena. Villarroel et al. (2022) constrained the source altitude to ∼42 000 km (geosynchronous orbit) through an Earth-shadow deficit. This paper presents two results. First, a pre-registered empirical test reveals the full temporal recovery profile: transient rates remain suppressed at 55% of baseline during days 7-21 post-storm, then rise to 309% of baseline during days 25-45 (p = 0.00066, Wilcoxon rank-sum; all robustness checks significant). Combined with the doseresponse staircase, the overall significance reaches 3.6-4.7σ (Fisher's method, range reflecting sensitivity to the independence assumption). The suppression-overshootreturn profile is consistent with a mechanism that concentrates reflective material during storms and releases it into favorable conditions after a delay matching known plasmasphere refilling timescales.