Keep presenter clock running when opening external demo

[bux]

Is there an easy solution to have the presenter clock / timer still running even when the presenter tab is not open in the foreground e.g. when opening an external demo?

I will be doing a presentation with slidev in front of a live audience. Before that I only did remote presentations.
For the live session there will be one projection behind me.

To be able to see the presenter notes I will have the projector act as an external monitor and display the normal presentation on there. But for demos (links to e.g. codepen.io that are added to the slides) on an external page I want to switch from extending to mirroring the macbook display.
Whenever I open the demo in a new tab, the presentation clock/timer pauses due to the tab not being active.

The reason im starting to mirroring the display is, that I don't want to turn my head 180° to look at the projector image and have the rest of my body turned towards the laptop stand :)