Time-specific: necessity holds at an identified time.
Time-indefinite: necessity holds at some time not identified.
For example:
“When fuel burns in this engine, heat is produced at that occasion” specifies a qualifying occasion.
“At some point while the vehicle runs, heat is produced” does not say exactly when.
These illustrative claims clarify temporal specification; whether a real physical judgment is strictly necessary requires separate justification. Changing specified to unspecified does not itself alter the force of necessity.