Just double checking since I've never been in a position to use status for a free same day change before, the SDC window starts when check-in opens the day before your flight, not midnight the day of your flight flight? I'm using my AA status here but I'm assuming that part's the same as if I had AS status.

I'm looking at booking a cheaper morning flight and then trying to SDC to the flight I actually want later in the day, and the morning flight would require getting up earlier than I normally do, so I want to make sure I'll be able to know for sure before I go to bed the night before what time I need to get up.