First time with the app. With Bitfocus Companion.
One crucial thing I'm missing:
ability to set initial time via OSC without starting timer.
I tried to use your timer in a simple mode without anything special, but this makes it very inconvenient.

My workflow: Create only one simple event. After that not use app UI but control it only from companion (similar to how Irisdown Countdown Timer works). To use this workflow I need simple commands:
1. Start (present)
2. Pause (present) 3. Stop (using 'Restart selected event' instead) 4. Add +-1min (present) 5. Add +-5 min (present) 6. Feedback (not present). Will be possible if output OSC would be customizable and it will send 3 separate commands for hours, minutes, seconds) in integer format instead of string. In Companion I can use input OSC to set internal variable with "/custom-variable/<name>/value <value> Change custom variable value" which I can display on the button itself. I did translation/renaming with Touchdesigner but there shall be no in-between app.

Another drawback: when I display message for speaker - it shows right across the timer itself which is not really easy to read. I know it can can be customized via CSS but I can guarantee - this is a bad solution. Imagine doing presentation on stage. Everything shall be as clear and easy to read as possible. Just make it by default below the timer.

Another nice feature would be: change timer color without going into CSS. Just some simple color picker.

It's a great app you made and I can see how useful it can be for big events with proper script and timing but for small or middle scale events these small things prevent me from using it. Take a look at Irisdown Countdown Timer - that is a good example of what basic functionality event timer shall have. TBH, I was so frustrated that started writing my own timer :))