You said it’s a new iPad, so I assume it has nothing to do with battery cycles. So the first thing you should check is whether you are using the 12w power brick that comes with your iPad Air. Many people prefer using only one charger for both their iPhone and iPad. If you charge your iPad with your iPhone charger, which is only 5w, then approximately it would take more than twice as long to juice up your iPad, because the current capacity of the 5w charger is 2.4 times lower.
For the same reason, if you are charging your iPad via the USB port on your computer, then it would take even longer to charge the battery to 100%, because the standard current limit of a USB port is 0.5 amp, meaning it is only, at most, equivalent to a 2.5 w charger. Actually, I think if you really charge your iPad via the USB port, because the current limit is so low, your iPad might not get charged at all. It would simply display a Not Charging message.
Personally, I always use the 12w charger for both my iPad and iPhone. And I suggest you do so too. It only takes about 4 hours to charge my iPad from nearly empty to 100%. If your iPad still needs more than 5 hours for a full charge with the 12w charger, then I think it is simply a case of a faulty product, and you should contact apple to demand a refund.