How is downtime determined?
Downtime is determined as the amount of time between an alarm trigger (down) and the next alarm reset (up).
For example, if a Watch Item fails and is down at 1:00, then suceeds and is up at 1:20, the downtime is 0:20.
If there have been no failures, then the total running time is the uptime.
If there have been no successes, then the total running time is the downtime.