Use the TRANSIENT Durability QoS policy, but I don't want to receive such samples that were sent before the discovery process is complete

[yuzu-ogura]

Is there a timestamp value can be access from on_data_available() callback?

[JesusPoderoso]

Hi @yuzu-ogura, thanks for using Fast DDS.
The main purpose of the TRANSIENT DurabilityQoS is indeed to receive all the samples sent before.
Perhaps you would be interested in using the VOLATILE configuration instead. Refer to the Durability documentation section for more information.

Is there a timestamp value can be access from on_data_available() callback?

The SampleInfo data contains, among other key information as valid_data and instance_state, the source_timestamp and reception_timestamp values, which may be of your interest.