Is it possible to schedule table update/refresh in Oracle Application Express?
You can do the following steps in a procedure:
1) User UTL_HTTP to read the csv file;
2) Save the file on a oracle directory;
3) Create an external table that will map this CSV file;
4) Schedule this procedure accordingly, using dbms_job_scheduler

This assumes your user has permissions to execute UTL_HTTP, UTL_FILE and DBMS_JOB_SCHEDULER, besides read/write permission in the given oracle directory.