JVC uses very similar procedures for clock setting across a large range of models so there is a good possibility that your S16 is the same as is used for the S15 as is shown below.

To set the clock on model KD-S15.

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.