Nikon Z 5 Reference Manual page 142

3
Rotate the main command dial to choose a shutter
speed of Bulb ("Bulb") or Time ("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.
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.
The Mode Dial
100
Bulb Time