const CTimeSpan& operator +=( CTimeSpan timeSpan );
const CTimeSpan& operator –=( CTimeSpan timeSpan );
These operators allow you to add and subtract a CTimeSpan to and from this CTimeSpan.
CTimeSpan ts1( 10 ); // 10 seconds
CTimeSpan ts2( 100 ); // 100 seconds
ts2 -= ts1;
ASSERT( ts2.GetTotalSeconds() == 90 );