Edit:

TIMESTAMPUNIT can be used to specify the unit when a timestamp field is used, as suggested here

For example, this is saying that "I want to use the private_efdStamp field as the InfluxDB timestamp with microseconds precision":

INSERT INTO Test.logevent_heartbeat SELECT * FROM Test.logevent_heartbeat WITHTIMESTAMP private_efdStamp TIMESTAMPUNIT=MICROSECONDS

It would be nice to explain this possibility in the InfluxDB Sink connector documentation.

However, as discussed in PR #851, it doesn't work completely with double timestamps as this information also needs to be used to choose the multiplication factor before coercing it to Long.