When it takes a while for the do not unplug, it’s usually because it’s just still writing data. The loading bar you see is actually writing to a cache. If you run sync after copying the data, you’ll probably find that it finishes at the same time that it says it’s safe to unplug. The easy solution is to just get faster / nicer USB drives - check reviews for benchmarks if you can find them.
When it takes a while for the do not unplug, it’s usually because it’s just still writing data. The loading bar you see is actually writing to a cache. If you run sync after copying the data, you’ll probably find that it finishes at the same time that it says it’s safe to unplug. The easy solution is to just get faster / nicer USB drives - check reviews for benchmarks if you can find them.