timestamp property
The timestamp when this message was sent or retrieved.
For incoming messages from a BroadcastReceiver, this corresponds to the time at which a message was received.
For outgoing messages, this is set during sendBroadcast. If the receiver of the sent message also uses this package, the send timestamp is available in data and the receive timestamp is set to this field.
The reason for this is that neither Android, nor iOS provide a standardized way for message timestamps. Therefore, the described logic tries its best to record consistent timestamps. If you rely on this information, you should also check the docs for the messages you receive for hints about timestamps.
Implementation
final DateTime? timestamp;