AWS SDK - When iterating shards with ShardIteratorType.AT_TIMESTAMP, what is the datetime stamp stored in the data record?

According to the KDS API documentation, specifying a ShardIteratorType of AT_TIMESTAMP "starts reading from the position denoted by a specific time stamp, provided in the value Timestamp." "Timestamp" is defined as "the time stamp of the data record from which to start reading."

Time stamp of the data record ... is this the same time stamp that can be retrieved from the record via Record.getApproximateArrivalTimestamp()?

If so, is this a useful value for checkpointing, given that (again from KDS documentation) "there are no guarantees about the timestamp accuracy, or that the timestamp is always increasing. For example, records in a shard or across a stream might have timestamps that are out of order" ?

Thanks in advance.