This PmTimeDate records when the current adjustment interval's high watermark value was set, per its DESCRIPTION, returning an empty string if no watermark has been established yet in this interval. Because the high watermark is what actually gets compared against the upper/lower boundaries at end-of-interval to decide whether a TCA fires, this timestamp tells you exactly when during the interval the worst reading occurred, which is what you'd check first when investigating why a TCA fired -- was it a brief spike early in the interval that then recovered, or a value that stayed bad right up to the evaluation moment. For example, a watermark timestamp only seconds before IntervalEndTime suggests the bad reading was still current when evaluated, whereas one from early in the interval that has since improved suggests the underlying problem may already be resolving.