re: "How long time must pass the 10% fee be?"
It happens automatically. As soon as you pass the $500 mark for an individual client.
You don't need to worry about it or do anything to make it happen.
Also, something that is helpful, is Upwork sends a notice to you when you pass the $500 mark. You might not receive the notice the second you pass $500. But you'll receive it within a few days of hitting that mark.