With a CTimeSpan object you have to define the time span.
So you still need to calculate how many days/hours/minutes/seconds have passed before you use it. This will only tell him how many seconds are in a time span, not calculate the difference from start to end to give him the time span.
// example for CTimeSpan::GetTotalHours
CTimeSpan ts( 3, 1, 5, 12 ); // 3 days, 1 hour, 5 min, and 12 sec
ASSERT( ts.GetTotalHours() == 73 );
ASSERT( ts.GetTotalMinutes() == 4385 );
ASSERT( ts.GetTotalSeconds() == 263112 );