How to turn on/off iPad screen at specific clock times?
There isn't much you can do seen as your iPad is 5 major versions behind, and back then, there wasn't any reasonable way to do any kind of automations that would allow for what you need. So, in your case, unless you get a newer iPad, there isn't much you can do.
In the latest version of iOS though, you could use the shortcuts app to create an automation at 10am and 6pm to change the screen brightness.