This is it exactly as from the manual / Setting the clock on the KD-S15 unit. Press and hold the [SEL] button to enter basic settings menu. Press the fast forward button to select ‘CLOCK H’. Turn the control knob to set hour. Press the fast forward button to select ‘CLOCK M’. Turn the control knob to set minutes. Press and hold the [SEL] button to exit basic settings menu.

The KD-S13 as far as I can remember is similar to the 15, if indeed it is this is the procedure. I will see if I have a manual for the S15 and if so will send it as a PDF format file. Set clock on KD-S13. Hold SEL Button. Select item with up and down rectangular button on the right side of radio. Set or adjust with volume knob. Push SEL when finished.