Objectives Real-time knowledge of the system time offsets between different global navigation satellite system (GNSS) time references is a prerequisite for multi-GNSS joint navigation, positioning, and timing. This study aims to improve the accuracy of time offset monitoring and overcome limitations of existing models, such as incomplete delay correction.

Methods A monitoring method utilizing a standard one pulse per second (PPS) signal is proposed. The process involves constructing a hardware platform with high-performance equipment and performing precise calibration of the monitoring link. Subsequently, systematic errors such as time delay are optimized through closed-loop monitoring based on ground-based time and frequency signal sources, and the time offset data are processed with a dedicated algorithm. Furthermore, an evaluation strategy integrating both time-frequency and precision characteristics is established. This strategy assesses the time offset results by calculating their accuracy, drift rate, and short-term stability, with the latter quantified by the modified hadamard variance, alongside the uncertainty of the corresponding fitting residuals.

Results The monitoring and analysis results demonstrate that the new method achieves a measurement uncertainty of better than 3 ns for the time offsets between other major GNSS system times. Its accuracy is, on average, four times higher than that of the single-point positioning method. The proposed evaluation strategy enables a comprehensive system analysis by considering both the time-frequency and precision characteristics of the results.

Conclusions The proposed framework, integrating the modified one PPS calibration, closed-loop monitoring between the received spatial signal and the corresponding ground-based time frequency signal, and a dedicated data processing algorithm, enables real-time, high-precision GNSS time offset monitoring. The accompanying evaluation strategy provides a scientific and effective means for multi-faceted result analysis. The results confirm that BDT maintains good consistency with other GNSS time references.