I think the D3s has a battery for the clock. It should be in the user manual
https://www.nikonimgsupport.com/na/NSG_article?articleNo=000026890&configured=1&lang=en_SGReplacing D3 Camera Clock battery
Nikon D3 has a lithium battery (CR1616) powering the camera clock with a lifespan of about 4 years.
If the ‘CLOCK’ icon is displayed in the top control panel while the exposure meters are on, the battery is running low and needs to be replaced.
When the battery is exhausted, the ‘CLOCK’ icon will blink while the exposure meters are on. Photographs can still be taken but will not be stamped with the correct time and date, and interval timer photography will not function correctly.
Replace the battery as described below:
Remove the main battery.
The clock battery chamber is located on the roof of the main battery chamber. Turn the camera off and remove the EN-EL-4a battery
Open the clock battery chamber.
Slide the clock battery chamber cover towards the front of the main battery chamber.
Remove the clock battery.
Insert the replacement battery.
Insert a new CR1616 lithium battery so that the positive side (the side marked with “+” and the battery name) is visible.
Close the clock battery chamber.
Slide the clock battery chamber cover towards the back of the main battery chamber until it clicks into place.
Replace the main battery.
Reinsert the EN-EL4a.
Set the camera clock.
Set the camera to the current date and time. Until the date and time have been set, the “CLOCK” icon will flash in the top control panel.
