Echoing Lassi above, I'm going to strongly argue this is
*fantastically* beyond the remit of a SRFI-170 implementor.
Actually, what's really needed is the timezone *root*, since the date-time SRFI needs to be able to find the timezone files themselves. They could be almost anywhere on Windows, which does not provide them standard (but they are available with a Java or Python installation and can be installed stand-alone if need be). So flush current-timezone.
Unfortunately, none of the <time.h> variables are useful to us:
> extern int daylight;
This is a weird flag where 0 means 'never does daylight time' and 1 means 'sometimes does daylight time'.
> extern long timezone;
This is the current offset from local *standard* time to UTC.
> extern char *tzname;
This is the name of the current offset, not timezone, like EST for the U.S. or Australian east coast. It's only useful for date formatting.