How long should it take to fully charge an iPhone 4S battery?

This is my first iPhone and I've noiticed that when I charge it from empty (trying to solve the famous battery issue with the iPhone 4S) that charging times from 0%, where the phone shuts itself off to 100% charge only takes about 45mins or so when using the supplied cable and power adaptor. Is this normal?

I looked here:

http://support.apple.com/kb/ht1476

But it doesn't say how long it should take to charge fully.

Nor does it mention it here:

http://www.apple.com/batteries/iphone.html

So, it's ≈ 45 mins normal to go from 0% to 100%?

I've noticed that my iPad2 takes far longer to charge than my iPhone 4S, but it is a bigger battery.