According to the above comments you seem to have a time span string in the format hh:mm:ss. Then you can perform the conversion like this:
COleDateTimeSpan SpanFromString(const CString& strSpan) const
{
long lDays = 0;
long lHours = 0;
int nMins = 0;
int nSecs = 0;
LPCTSTR s1 = strSpan.GetString();
LPCTSTR s2 = _tcschr(s1, _T(':'));
LPCTSTR s3 = s2 ? _tcschr(s2 + 1, _T(':')) : NULL;
if (s3)
{
nSecs = _tstoi(s3 + 1);
nMins = _tstoi(s2 + 1);
lHours = _tstol(s1);
}
else if (s2)
{
nSecs = _tstoi(s2 + 1);
nMins = _tstoi(s1);
}
else
nSecs = _tstoi(s1);
if (lHours >= 24)
{
lDays = lHours / 24;
lHours %= 24;
}
return COleDateTimeSpan(lDays, (int)lHours, nMins, nSecs);
}