12 hours of pretty high usage, wifi, LTE, internet browsing
Just remember that Apples numbers are sort of like a guide to compare with. 12 hours of pretty heavy use is darn good.
In a week or two when you are playing less is will be better. If after a week you are still using your device that much you need to face the facts that you might need to top off the battery sometimes during the day.
You might also get a hobby, like working.