Contacted support regarding this. Their answer:

Since the database is managed on our end it isn’t possible to access the cluster to enable slow_query_log directly.

The general_log and slow_query_log_file can be seen under the “Queries” sub-tab of your database cluster.

The long_query_time is set to 10.000000

Regarding changing long_query_time:

Currently, it is not possible to edit the the same. We are looking at this for the future but at this time it’s not possible.