How many days does a criminal background check?

This really depends...On the country in which you do the background check, on the depth required in the search (some checks only look for convictions, some look into more detail, such as an arrest record, charge, or acquittal), and also on the type of organization conducting the criminal background check.

I know that in Canada, there are private services available that provide some results in as little as one hour, but more commonly it takes 24-72 hours, although this is no guarantee.

However, if the RCMP is conducting a criminal background check (it will be a very in depth check) it can take anywhere from 120 days (for people who have no criminal record) to over 120 days (for people who do have a criminal record).

Basically, it can take as little as 1 hour for surface information, or as long as 3+months for an extremely detailed check.

As I said, I'm sure the waiting times vary for other countries, but this should provide a guideline. Hope it helps!