>>If so, depending on the kind of light you had where you were shooting, exposures will often be several minutes.<<
That makes me wonder if I'll see much of anything at all on my film. There was a little light in places (streetlights in a parking lot, and an occasional window light) but not much. I don't think any of my exposures were even as long as 1 minute. I'll see what I get when I get into the darkroom, and try again.
I love the tip about the black card when cars pass. That was a challenge as we tried it without dark cover over the lens.
Thank you all!
Now off to photograph friends rounding up cattle to take to auction... in daylight.