According to the Institute for the Study of War, per its September 8 report: "Ukrainian forces will likely capture Kupyansk in the next 72 hours, severely degrading but not completely severing Russian ground lines of communication (GLOCs) to Izyum."

If there is confirmation before the end of September 12 that they captured the town before the end of September 11, the question resolves to "YES". Otherwise, "NO". The question only closes 24 hours after the end of September 11, because it can take a few hours for a town's capture to be confirmed after it has actually happened.