I am currently have a U class ticket for Friday between YSJ and YYZ as follows:

YSJ-YHZ FT 7484 Class U
YHZ-YYZ FT 109 Class U-confirmed upgrade C

Is is possible to use the YSJ-YHZ portion on Thursday 11th afternoon by showing up and getting on the flight standy since it is a changeable ticket and still use the YHZ-YYZ portion on the 12th of December?

Or do these flights have to be taken in the same day as per my ticket?

Any help is appreciated.