We found out we can't trust second behind master since it's not accurate.
So instead we add heartbeat table to our database and monitor it by send heartbeat every 10 second it helps us to understand the lag
We see big difference
We have something which consuming the heartbeat topic and tell us how far are we behind the master.
The reason I am telling you that is I think you should have something like this in debezium
Especially if people are using it to sync between MySQL to other data sources
I can show you dashboard different between heartbeat metrics and second behind master

as you can see seconds behind master report about lag in hours must be because it calculate not only the white list data
whereas heartbeat get a better lag in minutes and more precise since i know it is in the kafka already .