Long-term effectiveness of high-explosive devices necessitates maintaining a level of specific surface area of initiating powder components within specified margins. This ensures that ignition and detonation performance of the powder does not degrade significantly over time. Flow permeametry is a commonly employed surface characterization tool in this context, as embodied in the Fisher sub-sieve surface area (FSSA). Recently we made alterations to the commercial permeametry apparatus that enables accurate in situ measurements of FSSA using only similar to 100 mg samples. In this work we report on a 24-month aging study in such modified sample holders at elevated temperatures of 40 degrees C and 60 degrees C. Through a process called time-temperature-superposition (TTS) the resulting isotherms are translated into a single master curve that predicts powder FSSA evolution over decades under ambient temperature conditions. We generate master curves for two different powders, i.e., pure PETN and 1 wt% added TriPEON, and show that the TriPEON-doped powder coarsens at a rate a few times slower than the non-doped powder. Activation barriers computed from the TTS shift factors shed some light on the coarsening mechanisms.