scmJS docs

Set Countdown Timer

Sets the countdown timer shown at the top of the screen, adds to it or takes from it, in seconds. Countdown Timer tests it.

Action 14 · Set Countdown Timer(Modifier, Seconds);

Argument Takes Stored in the action
Modifier Set To, Add or Subtract byte 27
Seconds a number of seconds bytes 12–15
Set Countdown Timer(Set To, 300);