It was a long day, one of the last images is shown below. The Canon 5DS / 5DSR are complex cameras with more menu options than ever. I had to really study things out to get the camera configured the way I wanted it (Canon 5D Mark III much easier)—a real head scratcher for a while, with one critical AF option not even in the AF menu section—not well done.
Canon offers a timed bulb exposure: with the camera in Bulb mode, enable the Timed Bulb setting, dial in the desired exposure (to the second and up to hours long), press the button and walk away—job done. This is very handy, a pity that Nikon didn’t do it like Canon has; Nikon T-mode forces you to time the exposure yourself and press the button yourself, incredible as it seems (unless I've incredibly somehow missed something). There is still room for improvement with Canon—why is exposure arbitrarily limited to 30 sec anyway? The Ricoh GR allows directly choosing up to 5 minutes with no foolin' around with special settings or modes.
Update: reader Mike H points out that the Nikon D810a astrophotography-oriented model has a “timed bulb” feature. Hopefully this will make it into a D810 firmware update.