It's the system time of the actual (virtual) server. Depending on where it is and where you are there may very well be a difference. Changing it will potentially lead to a whole heap of other problems depending on what else that server is doing so I wouldn't want to take that step too lightly.

FME Server/Flow uses the time zone that is defined in the OS settings, so you'll have to look into how that is set (depends on the OS) and then restart all the FME services. Other than that, I agree with @Hans van der Maarel​ about considering other systems on the same server that might be impacted by this change.