Custom Timer

Is it possible to create custom countdown timer (HOUR:SEC) in storyline using javascript or any other way which will be shown on every slide seperately?

I should be able to set (or update) any time as and when required and timeline of that slide will end after the timer is over.

I want the timer to play automatically when timeline will start.For the time being i want it to be 20 minutes for each slide.The background of the timer should be transparent.It should start when user revisits the slide ot clicks try again.

Is it possible to increase / decrease the duration of timeline automatically when timer is updated?

I have attached my .story file

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