Remarks
It is not recommended that you add and subtract values from this structure to obtain relative times.
The following list shows tasks to perform instead:
Convert the SYSTEMTIME structure to a FILETIME structure.
Copy the resulting FILETIME structure to a ULARGE_INTEGER structure.
Use usual 64-bit arithmetic on the ULARGE_INTEGER value.
Millisecond granularity may not be supported by a hardware platform. The caller of this function should not rely on more than second granularity. It is not recommended that you add and subtract values from this structure to obtain relative times.
The following list shows tasks to perform instead:
Convert the SYSTEMTIME structure to a FILETIME structure.
Copy the resulting FILETIME structure to a ULARGE_INTEGER structure.
Use usual 64-bit arithmetic on the ULARGE_INTEGER value.