I've got a very specific question:
When a fire sensor perceives a fire, does it wait 20 or 60 seconds before giving the alarm?
The fire sensor's time to give the alarm is customizable depending upon the fire safety alarm being used. Two widely used types of continuous-loop systems are the thermistor type detectors, such as the Kidde and the Fenwal systems, and the pneumatic pressure detector, such as the Lingberg system. (Lindberg system is also known as Systron-Donner and, more recently, Meggitt Safety Systems.). A typical delay of 10 Seconds is quite common. Here is the Source for your further reading