Looker doesn't seem to respect 'time_zone' parameter in Bigquery JDBC connection string

[vfx1]

GCS documentation states time_zone can be used as JDBC connection string parameter. 

Testing Bigquery connection confirms:

Can connect
JDBC string: jdbc:BQDriver::xxxxxxx/looker_scratch?withServiceAccount=true&...&time_zone=Asia/Kolkata&readTimeout=240000&connectTimeout=240000&useLegacySql=false

Then running in SQL Runner

set @@time_zone="Asia/Kolkata";
select cast(current_timestamp as datetime)

produces different results with and without the first line (correct is SET is present).

Any thoughts why the JDBC param is ignored?