When a new user FIRST-TIME using LDAP credential to login,

Jenkins will create

<Jenkins_Install_DIR>/users/<USER_ID>/config.xml file,

and update LastGrantedAuthoritiesProperty attribute with the current timestamp:

 
<jenkins.security.LastGrantedAuthoritiesProperty>
<roles>
<string>authenticated</string>
</roles>
<timestamp>1548376473889</timestamp>
</jenkins.security.LastGrantedAuthoritiesProperty>

But any subsequent LDAP login,

the timestamp of LastGrantedAuthoritiesProperty is not updated anymore.