This is available on their site: the link to the US version is here.
What is my warranty after my console is serviced?
We provide a post-service warranty for serviced consoles. The length of the warranty depends on whether the service was in-warranty or out-of-warranty as follows:
In-warranty service: If your Xbox 360 console was serviced within the original warranty period (free repair), you receive either the balance of your original warranty or 90 days, whichever is longer.
Out-of-warranty service: If your Xbox 360 console was serviced out of the original warranty period (paid repair), your serviced console will have a 90-day warranty.
