stopwatch timed activity

i'm trying to create an activity where there are several things wrong within a picture and the user has only 30 seconds to click on all the wrong items (with each click, the timer stops, and a question pops up on a separate layer - once the user answers, the layer disappears and the timer resumes).

i need to be able to display the timer (preferably as a stopwatch, but i'm not picky) as it's counting down. and i need it to prompt the user if they're running out of time and still have several items left to find.

is storyline able to do this yet? i can't use a .swf timer because we want this course to run on iPhone and iPad without having to download Puffin.