DTC P2610 ECM / PCM Internal Engine Off Timer Performance: Description
WARNING: This page is about a different car, the 2006 Lexus GS 430. However, it is still accessible from the selected car via links, so may be relevant.
The soak timer is built into the ECM. To ensure that the EVAP monitor values will be accurate, the soak timer counts 5 hours (+-15 minutes) from when the engine switch is turned off. This allows the fuel to cool down, which stabilizes the Fuel Tank Pressure (FTP). When approximately 5 hours have passed, the ECM turns ON.