CueTimer 2.5.0.18

Easy for the operator
Make a list of timers and edit them on the fly as the event progresses. If you need more hands on control with physical buttons, use Companion with Stream Deck. This also lets you remote-control CueTimer over the local network.
Useful to the speaker
Display the countdown on different devices: connect to an external monitor, send the countdown over the local network using NDI, or share a web-link to a remote speaker. The style of the countdown-window is customisable with fonts, logo and colors.
Broadcast reliability
CueTimer is a show-critical tool that you can trust for live events: The desktop apps use native frameworks for Mac and PC, giving us the best possible control of how the software performs on the hardware. It also lets you run the app without Internet-connection.
Home Page-

https://www.presentationtools.com/cuetimer/