[Discuss-gnuradio] Timestamp 'rx_time' in Metadata

Hi

I have several questions regarding the rx_time in the metadata file sink, https://gnuradio.org/doc/doxygen/page_metadata.html

1) What is exactly the timestamp? The moment first sample is recorded on the hard drive? 

2) Is there an example to convert rx_time to readable format?

3) Is there an way to timestamp the IQ data at the moment they are generated by USRP? 

Thanks.

Zhongyuan Zhao