Thanks for the link. It really excited me, as it appears to do precisely what I want. Unfortunately, my camera (the ancient 1DMkII) is one of the cameras that they say won't work in HDR mode with this gizmo. Since I cannot afford to upgrade the camera and it is satisfactory for the rest of my shooting (although with noise-reduction software required after high ISO shots). If I had a newer camera I would grab the new timer, as it seems to be just what the doctor ordered.
I can only hope that somebody will still come up with a way of doing what I need in some of my HDR shots.
As far as bracketing intervals go, I wrote that at night I use sequences that are 1 2/3 stops apart, not 2/3 stops apart. I could use 2 stops, but I found that in areas with bright or specular highlights I get fewer of the little black areas in the midst of the highlights by the slightly smaller difference in bracketing.
My solution right now will be to up the ISO from 100 to 200 or more for those shots requiring shutter speeds over 30sec. Thanks for all of the responses.