What's the best way to make a same day change from an early morning flight to something later? I have a friend who's booked on YVR-YYC departing at 6:50 AM. She wants to fly later in the day. But, she doesn't want to have to show up at the airport before 6:50 AM to make the change!

Is it possible to miss the flight, and show up later to do a SDC to another flight that day? Are same day changes doable online? Basically, how can a SDC be done without going to the airport early in the morning?