Yes, a 4 hour charge is not excessive if the battery was exhausted and you have it on during the charge.
Originally Posted by Grinchy
And some folks like to charge it overnight or whilst they are out and about, so no need to leave the iPad on whilst it is charging... It will in theory charge a little quicker if off, although in practice I'm not sure you would notice much difference... Turning it off is just a personal preference. As you point out, it's no good if you are desperate to know exactly when it is fully charged.
Hope that helps.