The SetDateTime method sets the current system time on the computer. On computer systems running Windows NT/2000, the calling ...

The SetDateTime method sets the current system time on the computer.  On computer systems running Windows NT/2000, the calling process must have the SE_SYSTEMTIME_NAME privilege.
The method returns an integer value that can be interpretted as follows: 
0 - Successful completion.
Other - For integer values other than those listed above, refer to Win32 error code documentation.