The right moment to ask for ratings:

• Only ask users that installed the app longer than seven days ago, making them returning users and increasing the chances they like the app.
• Ask for a rating once per app version to prevent asking to review the same app version multiple times.
• The user should have a minimum number of sessions or a certain time must be passed.
• Significant user events should’ve been triggered, indicating the user understands and uses the app.
• Wait until the user has accomplished something within your app or finished with his/her intended task. Prompting a review when users are feeling good about the app makes it a win-win situation for both the app developer and the end-user.

Notes: 

• The app review for rating prompt will only be displayed a maximum of three times within 365 days to a user.
• There is no possible way available to check whether the rating prompt showed up or not.
• You won't be notified of any activity taking place with the review popup. 
• Significant user events should’ve been triggered, indicating the user understands and uses the app.