I just copy - paste my code to get the difference between time. Hope it helps you.
SYSTEMTIME prCreateDateTimeSys;
prCreateDateTimeSys.wYear = GetIntFromString(strCreationDate,4,0);
prCreateDateTimeSys.wMonth = GetIntFromString(strCreationDate,2,4);
prCreateDateTimeSys.wDay = GetIntFromString(strCreationDate,2,6);
prCreateDateTimeSys.wHour = GetIntFromString(strCreationDate,2,8);
prCreateDateTimeSys.wMinute = GetIntFromString(strCreationDate,2,10);
prCreateDateTimeSys.wSecond = GetIntFromString(strCreationDate,2,12);
prCreateDateTimeSys.wMilliseconds = 0;
prCreateDateTimeSys.wDayOfWeek = 0;
COleDateTime prTimeCreated(prCreateDateTimeSys.wYear,prCreateDateTimeSys.wMonth,
prCreateDateTimeSys.wDay,prCreateDateTimeSys.wHour,prCreateDateTimeSys.wMinute,
prCreateDateTimeSys.wSecond);
COleDateTime prEndDateTimeSys = COleDateTime::GetCurrentTime();
COleDateTimeSpan timeDiff = prEndDateTimeSys - prTimeCreated;