Event Timestamp

An event timestamp is the time attached to each event saying exactly when that action happened; it is the backbone of any time-based analysis and of event ordering.

A timestamp looks simple but carries three ambiguities that can wreck analysis. First, event time differs from insert time: an event created offline has an old occurrence time even though it reached the server later. Second, time zone: if the time is stamped by the user's device clock and that clock is wrong or in another zone, the event lands on the wrong day, which is why most systems normalize time to a single basis. Third, that same time gap produces out-of-order events, where arrival order is not occurrence order and reconstructing the user's path gets harder. The practical upshot: when a trend chart shows a strange spike on one day, the first check is whether the spike is real and not an artifact of an offline timestamp or a time zone.