Shameless plug: I wrote a little Python timer for Linux that works great with a dropdown terminal like Yakuake: https://github.com/krotera/timerBeetle

I often use it for timed tasks, and it's faster than reaching for my phone or even opening a browser tab (and, unlike a Google or DDG timer, it doesn't keep ringing until you re-raise the browser window, find the tab, and silence it, which always annoyed me). : p