Nikon D780 Reference Manual page 78

D
The B ("Clock Not Set") Icon
Flashing B icon in the control panel indicates that the camera clock
has been reset. The date and time recorded with new photographs will
not be correct; use the [Time zone and date] > [Date and time] item in
the setup menu to set the clock to the correct time and date. The camera
clock is powered by an independent clock battery. The clock battery
charges when the main battery is inserted or the camera is powered by an
optional power connector and AC adapter. It takes about 2 days to
charge. Once charged, it will power the clock for about a month.
A
SnapBridge
Use the SnapBridge app to synchronize the camera clock
with the clock on a smartphone or tablet (smart device). See
SnapBridge online help for details.
First Steps
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