So just thinking through this I think I have a way you can accomplish this. You will need to create a number Field on the user called something like “ad-count.” Now identify a few screens or actions that you would like to trigger the ad pop up. Ideally some very commonly used actions like going to a main element or user page. This will depend on your app.
Now add an action to those interactions or screens that increment the ad-count field +1 every time those actions are taken or a screen is viewed. Next you will create an action link to your ad pop-up screen with a filter to only do this when the “ad-count” = 5(or whatever you choose).
This will make it so when a user takes your desired actions or views your screens X number of times, they will the be directed to the ad pop up screen.
On the ad pop up screen, add a screen action the resets the user “ad-count” field back to zero. This will the reset the counter and they won’t see your ad again till they have interacted with your app the desired number of times again.
That should get you close to what you are looking for, but I am not sure of a great way to time it, because I think the timer actions will only work from the screen they are on. But you could definitely investigate with something similar to above, but with a time and actions to set and reset the time when the ad is displayed.
Hope this helps!