Nikon Z 8 Reference Manual page 127

3
Rotate the main command dial to choose a shutter speed of Bulb ("Bulb") or Time
("Time").
Note that the exposure indicators are not displayed at a shutter speed of Bulb or Time.
4
Focus and start the exposure.
"Bulb": Press the shutter-release button all the way down to start the exposure. Keep the
shutter-release button pressed during the exposure.
"Time": Press the shutter-release button all the way down to start the exposure.
The elapsed time is shown in the control panel.
5
End the exposure.
"Bulb": Lift your finger from the shutter-release button.
"Time": Press the shutter-release button all the way down a second time.
Bulb
127
Time
Exposure