There is local time and base time. As you understand, base time is what your home port runs on. Local time is the time zone conversion of your current location. Since the game apparently does not have a "math" function for that, it is not displayed anywhere. However, if you do a Single Mission, you will then run on "Local Time" from where the scenario starts... Maybe someday we'll try to get a 2nd or 3rd clock on the sub and attempt to "offset" the hands, but we wouldn't be able to label them, since it is unknown which "base" your base time would be running from. It would be nice if the game had "Pearl Time", "Tokyo Time", etc., that we could reach out and touch...
Now, be aware that v-sync can mess with some video cards, which is why we now have that setting un-ticked by default. It is up to the player to decide whether to use it or not. Some nVidia cards, especially the older ones can be set to 1/2 frame if running at 60Hz, which then will make the card run at 30Hz, which is very close to the US video rate. The newer cards will end up with a multiple of their "clock". btw, I am absolutely awful with terminology. We really should have Front Runner pop in and post something on "refresh rate versus sync and / or frame rate etc"... hint-hint if you're watching!!! lol
(man, that's a puke-ugly green!)
Like KaleunMarco says above, check your settings in both places. Do remember though, that your boat still will not use much fuel. Trying to balance the handling (including dive & surface times), fuel, battery use, charge time, etc., is a royal pain. We might get back to that aspect some day, but not for a while.