Context of use restrictions only allow the following extension to be applied on Patient.birthDate: https://build.fhir.org/ig/HL7/fhir-extensions/StructureDefinition-patient-birthTime.html

Please update the context to allow it to be applied to Person.birthDate

We are building out our profiles for Person in Canada and need to express birthTime for unique person records and would like to use the globally recognized extension. 

There are a few other examples that maintain the patient- prefix in the extension while expanding context targets to person (see patient-proficiency)