Gisle Vanem came up with a nice little work-around for bug #1230118. It

seems the Windows (MSVC) libc time functions may return data one hour off if
TZ is not set and automatic DST adjustment is enabled. This made
curl_getdate() return wrong value, and it also concerned internal cookie
expirations etc.

lib/parsedate.c

@@ -236,9 +236,20 @@ static time_t Curl_parsedate(const char *date)
   struct tm tm;
   enum assume dignext = DATE_MDAY;
   const char *indate = date; /* save the original pointer */
-
   int part = 0; /* max 6 parts */
 
+#ifdef WIN32
+  /*
+   * On Windows, we need an odd work-around for the case when no TZ variable
+   * is set. If it isn't set and "automatic DST adjustment" is enabled, the
+   * time functions below will return values one hour off! As reported and
+   * investigated in bug report #1230118.
+  */
+  const char *env = getenv("TZ");
+  if(!env)
+    putenv("TZ=GMT");
+#endif
+
   while(*date && (part < 6)) {
     bool found=FALSE;