A batch in mParticle will contain different timestamps. Understanding the difference between the batch and event timestamp will help you be able to determine when events are logged via APIs or SDKs and when they are received by mParticle.
Event Timestamp
Outbound JSON will include an event_start_unixtime_ms field. In almost all cases this will be the same as the main event timestamp_unixtime_ms field.
Batch Timestamp
mParticle adds a top-level batch timestamp — timestamp_unixtime_ms — representing the time the batch was received by mParticle. This field is created by mParticle and should not be set manually when sending data via the Events API.