###### Abstract  
Currently, the space segment of all the five satellite systems capable of providing precise time transfer services, namely BDS (including BDS-3 and BDS-2), GPS, GLONASS, Galileo, and Quasi-Zenith Satellite System (QZSS), has almost been fully deployed, which will definitely benefit the precise time transfer with satellite-based precise point positioning (PPP) technology. This study focuses on the latest performance of the BDS/GPS/GLONASS/Galileo/QZSS five-system combined PPP time transfer. The time transfer accuracy of the five-system integrated PPP was 0.061 ns, and the frequency stability was 1.24 \(\times\)\(10^{-13}\), 2.28 \(\times\)\(10^{-14}\), and 8.74 \(\times\)\(10^{-15}\) at an average time of \(10^{2}\), \(10^{3}\), and \(10^{4}\) s, respectively, which significantly outperforms the single-system cases. We also verified the outstanding time transfer performance of the five-system integrated PPP at locations with limited sky view. In addition, a method is proposed to mitigate the day-boundary jumps of inter-system bias (ISB) estimates by considering the difference in the satellite clock datums between  
transfer could be as accurate as the two-way satellite time and frequency transfer (TWSTFT). [PERSON] et al. [5] also assessed the performance of PPP time transfer based on the GPS data, and the result demonstrated that the frequency stability could reach 2 \(\times\) 10\({}^{-14}\) within a day. [PERSON] and [PERSON] [6] adopted the GPS PPP to realize the inter-station International Atomic Time (TAI) calculation between station UNSO and station PTB, and it was proved that the PPP would be fully capable of replacing the traditional time transfer technique. With the development and maturity of the GLONASS, Galileo, and BDS, many scholars focused on the application of other GNSSs in precise time transfer. [PERSON] et al. [7] successfully realized the PPP time transfer based on BDS-2 dual-frequency observations, and their results showed that the frequency stability could reach 5.59 \(\times\) 10\({}^{-14}\) when the average time was 15,360 s. [PERSON] et al. [8] rigorously investigated the influence of Inter-Frequency Code Bias (IFCB) on GLONASS-only PPP, and established a feasible GLONASS-only PPP time transfer model. [PERSON] et al. [9] evaluated the enhanced performance of Galileo-only PPP time transfer with a priori constraints of receiver coordinates and zenith tropospheric delays. With the gradual progress of the Multi-GNSS Experiment (MGEX), more and more scholars began to focus on the PPP time transfer performance of multi-GNSS combinations. [PERSON] and [PERSON] [10] adopted the PPP and CV methods for time transfer based on GPS/GLONASS dual-system observations. The results showed that the dual-system combination could improve the short-term frequency stability of both two methods as well as the time transfer accuracy of PPP method, but the accuracy of CV time transfer was not significantly affected. [PERSON] et al. [11] evaluated the performance of real-time PPP time transfer based on the GPS, GLONASS, and Galileo triple-system combination. The results showed that the GPS-only case performed better than the other single-system cases, and the triple-system case had the best time transfer performance. [PERSON] et al. [12] further assessed the performance improvement of the PPP time transfer based on the GPS/GLONASS/BDS-2/Galileo quad-system combination compared with the single-system cases, and the gain of PPP time transfer brought by a modified model considering the correlation of receiver clock offsets among epochs. The results showed that, compared with GPS-only, Galileo-only, and BDS-2-only cases, the frequency stability of the quad-system PPP time transfer could be improved by 20.3%, 45.4%, and 84.0%, respectively, and the application of the modified time transfer model could further improve the frequency stability. [PERSON] et al.