The maximum amount of days a review can take to appear again is 180.
When I finish a course and review it to the point that its last level will take 180 days to be reviewed again, I don’t think I need that course anymore (it’s not like I’m risking forgetting too much, since there may be many courses with the same words that course had), so I delete it and concentrate my time in other course. However, I am used to learning using the web version (can learn more words in one session than the app), but I am used to reviewing words on the app (since I can review while doing other things).
That’s why being able to see how long until the next review, like how you can see it in the web version, would be a very useful feature in the app.