From the Operator DSS when idle:

Press [ICM] + [FEAT] + [6] + [4]
Enter the time [HH MM] using the 24 hour military clock
Press [SPKR]
From the Attendant Console when idle:

Press [ETC] + [ETC] + [ETC] + [F1]
Enter the time [HH MM] using the 24 hour military clock
Press [RLS]