How to time SPARQL queries on an Oracle12c database?
If you have access to the server, use SQLPlus running on the server to invoke your query; that will eliminate the network delay.  To get somewhat precise timings, invoke these SQL*Plus commands first:

set timing on
set autotrace on statistics


Invoke the SQL a few times; the first time will likely cache the data and subsequent runs will reflect that.  Then do the same queries via your client.

If you had DBA access you could turn on tracing for a session and see exactly how much time is used for each part of the query.