So I'm thinking about this.

Let's say I'm booked YVR - YYZ - BOS return; YVR-YYZ red-eye with an AM connection to BOS.

Let's say I want to go to a meeting in Toronto and want to take the BOS connection later. Can I same day change at YYZ if my itinerary has already started?

Essentially, I am curious if this process is legal:

1. Check-in and fly YVR-YYZ as scheduled.
2. Land at YYZ. Make SDC for later flight to BOS.
3. Leave airport, go to meeting, come back from meeting.
4. Fly YYZ-BOS on later flight.
5. Fly BOS back to YVR return as scheduled.

I am aware it says "prior to departure" but does that mean departure of the itinerary, or departure of just the flight in question?

Thanks for any insight for anyone who has looked into this!

Best,
l.