This PmTimeDate is the timestamp of the most recent Adjustment TCA that fired specifically because an interval's high watermark ended up outside the upper/lower boundary region, per its DESCRIPTION, returning an empty string if no such event has ever occurred. This, together with the LastIntvlEndTca* snapshot objects that follow it, is effectively a one-slot 'last incident' record for the slower, end-of-interval TCA path specifically (as opposed to the faster overflow/underflow path), so an operator can see exactly when and under what conditions the most recent one happened without having to have been watching in real time. For example, this timestamp reading three weeks ago tells an operator that the end-of-interval boundary mechanism on this instance has been quiet since then, even if the faster overflow-count mechanism has been firing far more recently.