First two smoke alarms have to detect smoke or high temperatures, then you'll usually have an acoustic and visual for at least 10 seconds (usually a bit longer) before the CO2 is released. The duration of the alarming period usually depends (among other factors) on the size of the data center, and how long it takes to evacuate at a reasonable pace.

In a real situation you would have 30 seconds

Typically 30 seconds

Typically 30 seconds in buildings, and 60-90 seconds on ships.