While I appreciate that need, as a user this is the worst way to get me to review your app. Especially because so many of them aren't tuned for paying any attention at all to what their users are doing before prompting them. I had one app recently prompt me for a review before I'd even completed their "first time tutorial" slide deck. Not only do I not know enough at that point in time to even review the app, but if I was so inclined to click through at that moment it would have been to leave a review complaining about the practice rather than saying anything substantive about the app's functionality. But even when they're not that bad, they're almost always popping up when I open the app (the moment when I'm specifically intending to do something that I'm now being interrupted) or in the middle of some workflow. It's the same annoying behavior that web pop-up folks used to do too.

Personally, I'd rather see you add a small UI element somewhere, or a banner that appears briefly but critically doesn't cover up any controls. If you absolutely MUST use a pop up, you know when the best time to do that is? After I've completed some in app purchase. If I'm spending money on your product, chances are I'm moderately satisfied with it and feeling pretty good about it at that moment. Or if you don't have in app purchases, unless you've made a "content browsing only" app, you probably have some workflows that have a definite end state. Prompt me then, at the end of me doing what I've come to your app to do. But I've never once given a review / stars to any app that has interrupted me in the middle of or at the start of doing something.