I guess it would be possible to provide the timezone to use in the annotation (as a String?)
Thus we could use different validation groups according to the timezone we handle in the application.
In my case I have an interface ValidationGroupAwareEntity which permits to automatically add groups based on the content of the bean (through a Validator proxy). So if I see the country is FR, I can ask for a validation with group FR.class

Or maybe the timezone could be provided optionnally in the validation interface? Or maybe could be set in the validator?