Is Facebook's stock priced for perfection?

David Paul Morris | Bloomberg | Getty Images

There are only so many hours in a day.

Facebook investors may need to realize this.

On average, users spend more than 45 minutes on the platform, an unprecedented amount of time for a digital property and likely hard to extend much further.

At 1.5 billion members worldwide, there are only so many people on earth to recruit to the social network.

And with the shares up 20 percent this year and trading at more than 90 times trailing 12-month earnings, it may be the classic case of a stock priced for perfection, vulnerable to a pullback on any hiccup in growth.