In "Screen Time" (IOS) you can see how long you spend on social networking apps

Feature of the Instagram app. On your profile page -> hamburger menu -> the one with the clock. (I have all the texts in German. Maybe something about "activity" in the normal version?)

If he is using the Instagram app, and Apple screen time or similar android feature it can give you a report based on per app time.

Apple screen time breaks down the time you use each app very well.