Nikon 1 J3 Reference Manual page 59

Choose a shutter speed of "Bulb".
2
Press 2 to highlight shutter speed and
rotate the multi selector counterclock-
wise to select "Bulb".
3 Open the shutter.
After focusing, press the shutter-release button all the way
down. Keep the shutter-release button pressed until the
exposure is complete.
Close the shutter.
4
Take your finger off the shutter-release button.
Shooting ends automatically after about two minutes. Note that
some time may be required to record long exposures.
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