In the Flag resource for FHIR dstu2 , the period attribute identifies the Time period when flag is active
"period":
category
false
CodeableConcept
Clinical, administrative, etc.
"category":
status
code
active | inactive | entered-in-error
"status":
Partially deaf, Requires easy open caps, No permanent address, etc.
"code":
author
Reference
Flag creator
"author":
period
Period
Time period when flag is active
identifier
true
Identifier
Business identifier
"identifier":
encounter
Alert relevant during encounter
"encounter":
subject
Who/What is flag about?
"subject":