"ELECTRONIC DIGITAL CLOCK
When the radio is on, pressing the TIME button will allow you to select between displaying actual time continuously or information related to the mode which theradio is in (i.e. in Radio mode, the radio frequency is displayed.) When the radio is off, time will not be displayed unlessthe TIME button is pressed, and then the time will only be displayed for 5 seconds. This function will operate with the ignition switch in either the on or off positions.You can ask your dealer to enable the digital clock to be displayed continuously when the radio is off and the ignition switch is on".
From my 04 300m manual