If running Windows, it may be easier to download and use the build on the releases page.
You can set the font, font size, background color and foreground color by adjusting the settings. Click the toggle button at the bottom to show/hide the timer.
To select a media player to close at countdown end, click the Player button, then click the window of the media player and check the box that says "Fade audio and close player". Be sure to manually adjust the system volume prior to countdown. At countdown end, the system volume will fade, the media player will be closed, then the system volume will be reset to the level you manually adjusted it to.