https://support.apple.com/en-au/HT208982
With Screen Time, you can access real-time reports about how much time you spend on your iPhone and iPad, and set limits for what you want to manage.
Screen Time — a new feature of iOS 12 — lets you know how much time you and your kids spend on apps, websites, and more. This way, you can make more informed decisions about how you use your devices, and set limits if you’d like to. Read on to learn how to turn on Screen Time, view your report and set limits, and manage a child’s device.