It is inherently challenging to characterize long-period transiting exoplanets because the transit events are rare and last long. These systems provide unique insights into planetary formation, migration, the detection of exomoons, and primordial atmospheres by occupying a sparsely populated region of the exoplanet parameter space, however. The complexity increases further for long-period planets near mean-motion resonances, where transit timing variations (TTVs) can reach amplitudes of several hours to days. We present a coordinated space- and ground-based observing campaign using photometry from NEOSSat, multiple LCOGT sites, MuSCAT, MuSCAT3, Tierras, and NGTS to capture the 19-hour transit of the long-period giant exoplanet HIP 41378 f (P ≍ 542 d, R ≍ = 9.5 R⊕) on 31 October 2025. Our transit analysis constrains the time of inferior conjunction to TC = 2460980.888 ± 0.029 BJDTDB, occurring ∼7 hours earlier than predicted from its linear ephemeris. This significant offset is consistent with the previously reported TTVs of HIP 41378 f, confirming it as the longest-period exoplanet known to exhibit measurable TTVs. By combining this new precise measurement with the transit timings of the two outer planets in the system (HIP 41378 d and HIP 41378 e), we performed a dynamical modeling of the system using the N-body integrator TRADES, refined the ephemeris of HIP 41378 f, and predict future transit events for all three outer transiting planets.