Disabling DBMS_SCHEDULER queue
I can't test it right now but I think you could do this with open/close scheduler window:


first define a window with DBMS_SCHEDULER.create_window. This window could have a 24 hour duration and repeat every day so that it is always open.
modify your job submission so that they run under this window (parameter schedule_name of the DBMS_SCHEDULER.create_job procedure).
when you need to enter maintenance and/or release resource, use DBMS_SCHEDULER.close_window. When your maintenance is done, use DBMS_SCHEDULER.open_window.


The jobs submitted while the window is closed should be queued and run later when the window is opened.