Without status on DL, your options are either to change your ticket (be sure that it is reissued, not just the reservation changed) in advance or to call (or ask at the airport) three hours before the flight you want and ask to SDC for $50. Officially, standby is only allowed for elites.

I would expect Sunday to be a wild travel day, with airport lines and probably long hold times on the telephone general lines. Even worse, DL automatically hangs up rather than putting the call on hold when they are very busy.