As per the discussion here: https://github.com/open-telemetry/opentelemetry-python/pull/835#discussion_r465749433 The OTLP MetricExporter must send `start_time_unix_nano` and `time_unix_nano`
As per the discussion here: #835 (comment)
The OTLP MetricExporter must send
start_time_unix_nanoandtime_unix_nano