  The last few years have seen gamma-ray astronomy maturing and advancing in
the field of time-domain astronomy, utilizing source variability on timescales
over many orders of magnitudes, from a decade down to a few minutes and
shorter, depending on the source. This review focuses on some of the key
science issues and conceptual developments concerning the timing
characteristics of active galactic nuclei (AGN) at gamma-ray energies. It
highlights the relevance of adequate statistical tools and illustrates that the
developments in the gamma-ray domain bear the potential to fundamentally deepen
our understanding of the nature of the emitting source and the link between
accretion dynamics, black hole physics, and jet ejection.
