From the above linked page, the time to guess a 4-digit password of numerals only, such as is used on every ATM in the world, is basically zero.
HTML:
Length Combinations Class A Class B Class C Class D Class E Class F
4 10,000 Instant Instant Instant Instant Instant Instant
However, this assumes that the site that you are trying to break into is going to allow you to try thousands of passwords in less than a second.
Fortunately banks have lock out procedures in place that will ignore any attempt to access the account using any password after something like 3 failed attempts.

So there is about 3/100 of 1% chance to guess the password before the account is locked out.
Of course, there are some common things that people do with their ATM PIN that will make them much easier to remember and also much easier to guess, such as using the 4 digits on the corners (1, 3, 7, and 9), the middle of each edge (2, 4, 6 and 8), down the middle, or one side (0, 2, 5, and 8; 0, 1, 4, and 7; 0, 3, 6, and 9).
So do yourself a favor and avoid those combinations. This is not to say that you should avoid using these digits (that would not leave anything to use!), only that you should avoid using any of these sets of digits. You can use a pair that are in one of these sets if you throw in a pair that are not in that same set, such as 1,7,5 and 8. (About now, something like 10,000 people are changing their ATM PINs that were 1758

)
Lockout procedures, unfortunately, do not apply to attempts to crack an encrypted file that is stored on your own harddrive, but then the available choices for the password is much greater than is available for ATM PINs.
So do yourself a favor and use a longer password with a mix of the character classes (UPPERCASE, lowercase, numerals, and special characters).