Clarify that optional timestamp means current time should be used. (#824)
Clarify that optional timestamp means current time should be used. (#824)

* Clarify that optional timestamp means current time should be used.

* Update specification/trace/api.md

Co-authored-by: John Watson <d68442e18ce20d695ea66d3988492d75bf602243@gmail.com>

Co-authored-by: Bogdan Drutu <1078cf414b2625a240b16392085d66580bb66f4d@splunk.com>
Co-authored-by: John Watson <d68442e18ce20d695ea66d3988492d75bf602243@gmail.com>
open-telemetry/opentelemetry-specification,open-telemetry/opentelemetry-specification