Operator controls standalone

Set time Minutes Seconds

Transport

Presets

Adjust live

Title appears at the top of the stage, updates as you type

On-air text

Palette

Custom colours normal ≤60s ≤10s 00:00 title

Background colour transparent is what OBS should see

Look Digit size 320px

Bar position Width 1200px — or drag the bar itself

Sound at zero Volume 70%

Quick edit type a time, tune a colour lighter or darker

Sync room not connected

Keyboard

Space start / pause R reset ↑ or + add 1 min ↓ or − take 1 min 1 5 min 2 10 min 3 15 min C cycle background G progress bar B test burst S test sound

In OBS, add a Browser Source pointing at this page with width 1920 and height 1080. The stage above is transparent; the checkerboard is a preview aid — turn it off before going live.
Multi-window sync: two copies of this page stay in sync only when they are open in the same browser — two Chrome tabs, or two Browser Sources inside the same OBS. OBS embeds its own Chromium, so an OBS source and a desktop Chrome window are separate browsers and will not see each other. Use OBS’s Interact window to drive the on-air copy. Different people on different computers each get their own independent timer.
Presets in the URL: ?m=10&s=30&label=BACK%20IN&end=WE%27RE%20LIVE&bar=1&size=320&autostart=1 — handy for wiring up several differently-configured sources.