Sensor heartbeat interval and offline detection

How exactly does the base station determine a sensor is non-responsive and mark it offline, I have seen another post which suggests the base station waits 24hrs before reporting an offline sensor, that's a very long interval for a security system.

I assume the sensors send a heartbeat at regular intervals and after a number of missed heartbeats the base station will indicate they are offline. I've had several sensors reported offline at the same time, presumably the scheduled time for the base station to check for missed heartbeats. So how often are the heartbeats, how many need to be missed and when will the base station indicate the sensor is offline?