The GetTickCount function retrieves the number of milliseconds that have elapsed since Windows was started.
DWORD GetTickCount(VOID)
Parameters
This function has no parameters.
Return Values
If the function succeeds, the return value is the number of milliseconds that have elapsed since Windows was started.
Remarks
The elapsed time is stored as a DWORD value. Therefore, the time will wrap around to zero if Windows is run continuously for 49.7 days.
Windows NT: To obtain the time elapsed since the computer was started, look up the System Up Time counter in the performance data in the registry key HKEY_PERFORMANCE_DATA. The value returned is an 8 byte value.