Pierre de Ponthiere, Lesve Photometry developer, reports that SGP produces DATE-OBS with a bunch of decimal digits. When the seconds end in .9999 or more nines, the ExposureStartTime becomes junk (Windows null struct 1601, etc.).
Edge condition extracting the seconds part, ending up with SYSTEMTIME with milliseconds part = 1000. Oops. The SystemTimeToFileTime() chokes, resulting in FILETIME of 0. into