Nikon D300 User Manual (en)

Multiple Exposure
Do not remove or replace the memory card while recording a multiple 
Live view (pg. 79) can not be used to record multiple exposures.
The information listed in the playback photo information display 
(including date of recording and camera orientation) is for the first shot in 
the multiple exposure.
If no operations are performed for 30 s after the monitor has turned off 
during playback or menu operations, shooting will end and a multiple 
exposure will be created from the exposures that have been recorded to 
that point.
Interval Timer Photography
If interval timer photography is activated before the first exposure is 
taken, the camera will record exposures at the selected interval until the 
number of exposures specified in the multiple exposure menu have been 
taken (the number of shots listed in the interval timer shooting menu is 
ignored). These exposures will then be recorded as a single photograph 
and multiple exposure mode and interval timer shooting will end. 
Cancelling multiple exposure cancels interval timer shooting.
Other Settings
While multiple exposure mode is in effect, memory cards can not be 
formatted and the following can not be changed: bracketing and 
shooting menu options other than [White balance] and [Interval timer 
shooting] (note that [Interval timer shooting] can only be adjusted before 
the first exposure is taken). The [Lock mirror up for cleaning] and [Dust off 
ref photo] options in the setup menu can not be used.