Abstract: When an earthquake occurs near the GPS time (GPST) day boundary, the day-boundary discontinuity (DBD) in GNSS precise products may affect the extraction of coseismic displacements. To address this issue, Wuhan University (WHU) has released aligned rapid precise products to mitigate the influence of DBD on dynamic positioning. Taking the 2024 Hualien earthquake in Taiwan, China as a case study, the final products from the Jet Propulsion Laboratory (JPL), the final products from the Center for Orbit Determination in Europe (CODE), and the rapid products from WHU are selected to construct two processing schemes with and without day-boundary alignment. First, the signal-in-space ranging error (SISRE) of different precise products at the day boundary is evaluated from the product perspective. Then, high-rate GNSS observations are used for dynamic positioning to extract coseismic displacements. The results show that the aligned WHU rapid products achieve the smallest mean SISRE of 4.2 mm, while the mean SISRE values of the JPL final products, CODE final products, and non-aligned WHU rapid products are 11.8 mm, 22.7 mm, and 48.8 mm, respectively. Using the aligned WHU rapid products, the positioning results remain continuous near the day boundary, whereas the other non-aligned products exhibit position jumps of about 3–5 cm at the day boundary. The analysis indicates that the day-boundary discontinuity of precise products affects the accuracy of coseismic displacement extraction from high-rate GNSS data near the day boundary, and the use of day-boundary-aligned precise products can effectively improve positioning continuity.