You issue this command:SHOW SLAVE STATUS -In the output, there is a value for Seconds_behind_master.

It is the time between the I/O thread receiving details of the master's last transaction and the time it was applied by the SQL thread.

It is the time between the most recent transaction written to the relay logs and the time it was committed on the master.

It is the time between the I/O thread receiving details of the master’s last transaction and the time it was written to the relay log on the slave.

It is the time between the most recent transaction applied by a SQL thread and the time it was committed on the master.