As a high-thermal-conductivity material, graphite is not only important in thermal management applications but also serves as a fundamental platform for exploring phonon hydrodynamics at elevated temperatures. However, the modeling and understanding of the spatiotemporal dynamics of heat pulse propagation in finite-sized graphite remain not yet established. In this work, we target this challenge by directly solving the transient phonon Boltzmann transport equation in real and reciprocal spaces as well as in temporal domain with first-principles input. We investigate the dynamics of both ballistic heat waves and second sound, and uncover the impact of temperature and isotope concentration. In the ballistic regime, the present computational framework accurately captures the ballistic peaks of various phonon branches propagating at distinct speeds, and reveals different “peak attenuation” effects induced by elevated temperatures and isotope scattering. In the hydrodynamic regime, we unveil the kinetic formation process of the second sound wave packet, and demonstrate an optimal temperature window around 100–120 K and the monotonic dissipative effect of isotope scattering. Therefore, this study provides not only a robust computational framework but also deeper physical insights for transient dynamics of heat pulse propagation in graphitic materials.