I added interstitial ad (+banner) to my app that contains one activity

Question

I added interstitial ad (+banner) to my app that contains one activity, no problem with banner but the interstitial ad shows only at app launch one time, my app don't contain any buttons or actions just a news reading app, what I want to do is showing the ad every 5mins when the user reading the news. I searched the similar questions but couldn't get it. here my code to load and show the ad :

https://code.sololearn.com/cYi51aKROCSL/?ref=app

Answer 1

Full code?