I understand the same day part of SDC.
What I was checking was whether I could make the request of the concierge a day in advance and they could process on the day of the flight.
As per my example, if I check in for my flight at 10.40pm PST tonight, I can (hopefully) make a SDC for tomorrows flight. But my option now is to stay awake after midnight to call AC or do the SDC sometime in the morning to make their calendar day requirement.