Here is how I would do this -- use dbms_job to run the job in the background in the database. Don't run it in the client (for hours and hours).

If you use dbms_job, and you instrument your stored procedures with calls to the dbms_application_info package, your client can monitor its progress by querying the v$session table. You can then show people how far the procedure is and allow the client to go about its work. Additionally -- to "stop" the running program, your client can simply insert a row into a table and your procedure can "look" for that row and stop when it sees it (or use DBMS_ALERT or any method to get a message to this other session).

Other then that, if you are really going to run this on the client, I would use 2 forms and 2 sessions. Using logic just like above - the first form would run the second form which would run the procedures. The first form would not be blocked. The first form can signal the other form via a DBMS_ALERT or insert into a message table to tell it to "stop". Additionally you would still use dbms_application_info to allow form1 to display the progress of form2.