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In this paper, the stability and repeatability of receiver-characteristic inter-system biases (ISBs) is assessed in low Earth orbit (LEO), analyzing the measurements collected by Bobcat-1, the CubeSat developed at Ohio University which completed its mission in April 2022 after 17 months in orbit. GNSS interoperability has been a goal in the past years. The current increasing interest in a number of applications which would benefit from it, such as those involving users in the high-altitude Space Service Volume (SSV), are making the topic more and more crucial. GNSS-to-GNSS time offsets, also referred to as GNSS inter-constellation time offsets or XYTOs, are among the critical parameters for full interoperability. Users with not enough satellites in view to solve for the user XYTOs at the receiver could benefit from estimates provided externally, assuming their receiver-characteristic ISBs being prior calibrated. The results shown in this paper suggest that GNSS-to-GNSS time offset measurement and monitoring exploiting LEO receivers can be feasible, leading to the concept of a master-clock in space.