This Unsigned32 (1..65535) field states the configured length, in minutes, of this measurement bin. Because this is today's still-open 24-hour PM window, which keeps growing through the day and resets only when the daily boundary rolls over, Duration is the denominator you need to turn any of the accompanying event or error counters into a rate (events per minute) for comparison against other bins of a different length. For example, a Duration of 15 on a History row means the counters in that row cover exactly a quarter hour, so 900 dropped frames in that row works out to roughly one drop per second on average.