"authtimestamp" attribute replication

Hello So I have initiated the lastbind overlay and have retrived the 'authtimestamp' attribute on openldap 2.4.30. What I found is that the timestamps on the attribute have different values on the master server and slave servers. Is there any way to fix this issue? An application developer wants to retreive this value to create a report on 90 days of inactivity for users and since the attribute has different vlaues on different servers the testing on the accuracy of the report is failing. Thank you.