Your code looks correct. Are you using the latest version of Prodigy? You can check by running prodigy stats on the command line. The global CSS option and classes were only added recently, so you'll need at least Prodigy v1.7.0. Also make sure that your prodigy.json doesn't include a "global_css" setting that overrides the recipe config.
No, this is something you'd have to write in JavaScript – we don't have an example of this, since it's a pretty specific implementation. But you can find examples of adding custom JavaScript to Prodigy in this thread and in the PRODIGY_README.html.
So in the JavaScript code you pass in as "javascript", you'd have to create the countdown, add it to the page and then call into Prodigy's helper functions when the countdown is up etc. None of this is specific to Prodigy and just regular Vanilla JavaScript – so if you haven't done this before, you can probably find someone else who can write that countdown script for you in JavaScript.