It goes wrong where you apply Dist/Speed=Time.
You have used 200kts for the time from now......300 miles away for 1 hr 17.2. It gives the wrong answer that does not apply. However an interesting way of looking at the problem. You didn't test the answer. 257.3 miles at 260kts takes just about an hour. At 200kts it takes 1 hr 17.2 minutes.