Downloading image files from the camera take a part of the time that can be used for exposures. I investigated how long this time is in some different situation. From the beginning only the Canon 6D DSLR camera but added today the Nikon D800. The last measurements done on a Raspberry Pi5 setup, at bottom of page 2.
Here are the setup and downloading time:
http://www.astrofriend.eu/astronomy/...-transfer.html
The Raspberry Pi5 together with the new 64 bit OS system makes it a lot faster.
Lars