If there isn't a big change while in standby, you're probably okay, and your battery life will return to normal when your usage returns to normal (after the novelty wears off). When you pick it back up, note how much battery life you have left again. You can also note how much battery life you have left and then put your iPad down for 20-40 minutes. In other words, if your battery feels like it's only lasting half as long, first ask yourself if you're using it twice as much.
Then the screen stays on, storage gets written, WI-Fi and maybe cellular radios stay lit up, and power gets consumed.
That's especially true with things like ProMotion or Apple Pencil, or the new drag and drop or augmented reality (AR) features. In addition to the system taking a while to really finish transferring everything over, we also tend to spend a long time playing with new iPads and features.
