The main feature of this addon is not the timer but the display of the countdown/remaining time on the toolbar icon, that it always is/stays visible.

Since the available space for individual addons on the toolbar is very limited i dont think that there is a good way to make multiple timers visible like this.

But if you have an idea that is technically do/viable, feel free to create a suggestion issue on the support site. I'll look it over.

Fun fact: If you know how to sideload addons, you can technically load this addon multiple times and that would allow you to have multiple timers visible and configurable at the same time.