broken Apple Watch band warranty

In the United States the warranty is for 12 months. It may vary in other countries.

Here is a link that may be of some assistance

https://checkcoverage.apple.com

You may also need to speak to Apple Support

https://getsupport.apple.com

You can talk to support but based on other posts I've read they say that a broken band isn't covered by the warranty and is considered physical damage.