How Long Can Facebook Be Down?

I had a unique experience one morning. Facebook was down. Thankfully, chaos did not ensue. (Nor did the police get called. That I know of anyway.)

We are all used to different sites on the internet being down. Pretty much every site has its periodic maintenance and so forth. But I could not believe my eyes when I saw that Facebook was down for periodic maintenance. (I should have taken a screenshot of the page.) Oh, I could believe Facebook could be down for periodic maintenance. Just not...