This is by no means a finished product. Yet, it might be useful for you. It also lacks documention :)

CountdownClock

A countdown clock. You can set an amount of time to count down, or you can set a time to count down to. Support up to 99hrs remaining, or until midnight when set with a time to count down to..

An online working version can be found here: https://countdown-timer-7seg.web.app/

Future features

• Autohide "hours" part when initial countdown is less than an hour.
• Limit input on the config page.
• Auto fill-in something useful on the config page.
• Add documentation and descriptive texts
• Set colors whether time has (almost) passed.
• Sync multiple timers (using Firebase)