Need help making a time machine for short film

Hi all,
I'm new here so please bear with any faux pas.

I'm shooting a short sci fi film on the 19th & 20th of November (2016) and a key element of the story is a small, self contained electromechanical machine that stops time. (The film is called Stop:Watch). I've really tried getting my head around the Arduino system, and looked at all sorts of videos to help set this up but I just don't get it.
So, I really need some help creating the countdown timer part of the machine. It counts down from 5 minutes and needs to be easily reset, as the takes will be less than 5 minutes each, and finishes at zero.
It also needs to be small enough to share space with a mechanical section, separate on/off button and other circuit boards (not connected, there for camouflage) and sit inside a wooden box internal dimensions 95mm x 95mm x 35mm (base) + 15mm (lid).

If anyone can help I'd be happy to talk further. Obviously I'd be willing to cover the expense of the parts needed and some contribution for your time. The film is self funded so the budget isn't massive but let me know what you think would be fair.

Thanks for reading this far.

Andrew

I sent you a message via PM.

I recently did a really fun project for a design firm in the UK and I've worked on props for independent films before, one of which was surprisingly similar to what you're looking for here.

Let's talk.

So, 7-segment display? You will need something big and bright. If it's science fiction, perhaps a ring of leds?

In any case, you want a start/stop button and an easy way to set the time - a pair of up/down buttons will do.

Another option would be displaying a countdown on a mobile phone and putting the phone behind a panel.