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I am near Houston, Central Time Zone, so I set TIMEZONE to 6001. It is 12:33 here, but the plot stamp shows 7:33. I also tried setting TIMEZONE to -6001, same problem.
OS? On Windows it appears that the value taken by the date field in the format %<\AcVar Date \f "yyyy-MM-dd HH:mm:ss">% is the raw value of the system clock, without applying a time zone offset. This is consistent with Window's default assumption that the local PC clock is the current zone time.
Linux (and Mac?) maintain the system clock at UTC and apply the local zone offset. Somewhat annoying to have to fiddle with the clock when switching between booting Windows and Linux. So if you've recently switched back and forth between the two, that may account for what you're seeing.
AIUI the TIMEZONE variable only affects the location of the "sun" when it is enabled as a light source. Could be wrong, though.
I am using Windows. I'm a one-man show here, I miss having an IT department to fix this stuff.
Not entirely sure if the OP is in fact referring to fields. But if that is the case, choosing one of the 'regional' date formats should solve things.