I would say once it's too dark for your camera to keep up without blurring, that's the level of darkness that's good. In your examples, I would say 1 and 2 are fine, but the last 4 are getting too blurry to be useful (#3 is okay...). Sure, you can vaguely see some features, but if there are signs, I can't read them.
In this sequence of mine, I started riding home at 16:55 in February. I finished at 17:34, sunset at 17:36.
This is the beginning:
This is right near the end, when I shut off the camera because I felt it was getting too dark:
Then again, I've had problems with blurring on reasonably bright days on hikes in the woods, so it's not easy to judge darkness. Our eyes are too good for that. But generally speaking, I find that between sunrise and sunset are good. If my bike GPS switches to night mode, I know it's probably too dark.
I know we say that anything is better than nothing, but if that anything is really blurry, I'm not too sure. Your last photo shows that the road is probably asphalt, but that's pretty much all you can get from it.