Abstract: Timing error is a critical factor influencing underwater target positioning and navigation accuracy, particularly in cross-domain unmanned surface vehicle/autonomous and remotely operated underwater vehicle (USV/ARV) systems, where it directly affects overall operational performance. This study develops a mathematical model of timing errors for USV/ARV mobile observation systems and analyzes their propagation under three scenarios: one-time pre-submersion timing, intermittent timing, and real-time timing. Monte Carlo simulations reveal that timing errors strongly depend on the adopted timing method; in one-time timing, crystal oscillator frequency drift is the dominant factor; in intermittent timing, errors increase with the timing interval, with different primary contributors at varying intervals; in real-time timing, system processing delay becomes the main source of error. The results highlight that improving timing accuracy and optimizing error compensation strategies are essential for achieving high-precision underwater target positioning and tracking, thereby offering both theoretical foundations and engineering guidance for the optimization of underwater positioning, navigation and timing systems.