Well if the bank is a privately owned company the owner can close up shop any time he/she wants as long as all of the companies business is finished. ie: pending transactions, ect
Common Sense
As many as they want. Banks (like any business) may close for any reason.
TedEx
I believe it is a maximum of 3 days. The reason=--too much money in checks does not get processed.
That is why banks are open the day after Thanksgiving.