How to stop a timer

OK so I have created a timer as below, timer starts as expected :) we have a long running process that runs in the background as a scheduled job and updates a context to show progress (get_progress_bar is a function that returns an HTML page with stats/progress on the job) now I can see that the v_progress variable gets to 100 and the code executes the end_progress_timer with no errors.... but the timer continues to expire .... how do you stop a timer??? :)

procedure start_progress_timer is

begin

api_timer.startTimer('progress_timer');

end;

procedure end_progress_timer is

begin

api_timer.stopTimer('progress_timer');

end;

procedure progress_timer_expired is

v_clob clob;

v_progress number;

begin

v_clob := get_progress_bar;

api_component.setvalue('progress.generatedemandprogress',v_clob);

select sys_context('generate_dp_progress_ctx','PROGRESS') into v_progress from dual;

if (v_progress = 100) then

end_progress_timer;

end if;

end;