This records the last time the counters in this bin were reset, whether manually or by an automatic rollover. A ClearedTime noticeably more recent than StartTime tells you someone, or some process, reset this specific bin's counters mid-interval, so the totals in the current, still-accumulating short interval bin for this PM instance reflect a shorter effective window than its nominal duration would suggest. For example, seeing ClearedTime just two minutes old on this in-progress short-interval bin that's supposed to be most of the way through its interval would be the reason its RxPkts total reads far lower than the port's usual traffic level.