With kids, and limited schedules, we have every night reserved before leaving home. To mitigate against the unexpected, we try to limit driving to max 4 hours on the longest days. Still, we have more than once arrived at campgrounds after 9pm.
This summer I broke the crank on my mountain bike one day. The next day, we had to find a bike shop in Butte, MT with the right part, who could do the work right then and there. Plus getting gas and groceries, and then had to high-tail it down to Yellowstone's Madison CG in the pounding rain. So yeah, we set up in the dark that night. But that's what makes it an adventure :)