Long-duration, high-pressure resistance measurements on highly-ordered pyrolytic graphite in a diamond-anvil cell show a sluggish phase transition occurring at ∼19 GPa, as evidenced by the time-dependent behavior of the sample resistance. The instantaneous resistance response to pressure adjustment shows a ∼10 GPa hysteresis that has been observed previously, rendering the conjectured direct relationship between resistance and phase-transition tentative. In contrast, the evolution of the resistance with time after the instantaneous response shows a systematic, reproducible, and distinct behavior, which allows reducing the uncertainty in transition pressure to ∼2 GPa. This largely reduced hysteresis shows explicitly that the phase transition is directly related to changes in electronic structure and resistance and establishes consistency with other commonly used experimental techniques to explore phase transitions at high pressures. We augment our experiments with first-principle density-functional theory computations to evaluate the pressure dependence of the electronic density of states of proposed candidate structures for the post-graphite phase.