I was just thinking about what this 24-hour period means. At the beginning, both the case and the AirPods are full. After eight hours of listening, you can charge them twice, and after the second charge, the case is empty. There's quite an imbalance between the case and the AirPods now.
But 8 hours is perfect. But, as I said before... I'm sure I can charge the case once within this 24-hour period.