Stir vinegar, thyme, honey, mustard, onion, and salt together in a small bowl. Pour in olive oil and whisk until combined.
Bring a large pot of water to boil. Add beans to boiling water and cook for 3 minutes, until bright green. Drain and quickly transfer to a bowl of ice water. Drain again and pat dry. Place cooked beans, oranges, dates and hazelnuts in a large bowl. Pour dressing over beans, toss and serve. Best served at room temperature.