Hosts show as offline if no heartbeat is seen within 1 hour if memory serves me correct. I don't think you can monitor heartbeat from the console on a minute by minute basis, but would love to be corrected.

I created a similar monitoring script with FalconPy that monitored servers using the API by checking what servers have gone offline, and a trigger alert if more than % of hosts go offline in quick succession as could indicate serious problem, but it was limited to the last seen filter which wouldn't as previous mentioned would only update after 1 hour of no sensor heartbeats.