Nikon Coolpix 100 - Manual (Page 27)

15 First Steps : Setting the Time and Date
ADJUST button
When you have finished setting the time and date, turn the camera off to put
the new settings into effect.
Note: The clock-calendar has its own internal power supply. Should you
notice that the clock is running extremely late, this is probably a sign that the
clock's battery needs to be replaced. Take the camera to your local Nikon
representative for servicing.