Here is a plugin that lets you add a event countdown timer and stop-watch to your website. My Time Keeper for WordPress comes with simple controls and lets you start, stop and pause the timer conveniently. You will be able to use this plugin for quizzes and practice tests on your website.
The plugin comes with a simple shortcode and various parameters, so you can turn on autoplay, disable control bar, and turn on/off the warning bell. Users have the option to redirect users to a specific URL after their time is up. This is a commercial plugin by a CodeCanyon developer.