Dell OptiPlex 990 (Early 2011) - Manual (Page 11)

Set PRTC
Under the Intel ME Platform Configuration menu select Set PRC and press .
Valid date range: 1/1/2004 to 1/4/2021. Setting the PRTC value is used for virtually maintaining PRTC during the power-off
(G3) state.
Type PRTC in GMT (UTC) format (YYYY:MM:DD:HH:MM:SS) and press .