D6: Extended Shutter Speeds (M) - Nikon D780 Reference Manual

d6: Extended Shutter Speeds (M)

Extend the range of shutter speeds available in mode M; the
slowest shutter speed available when [On] is selected is 900 s
(15 minutes). Extended shutter speeds can be used for pictures
of the night sky and in other situations that require that the
shutter remain open for long periods.
•
To use extended shutter speeds, choose [On] and select a
shutter speed of 60 s or slower.
610 Menu Guide > A Custom Settings
G button U A Custom Settings menu