You can query the Plesk database directly to get TTL values. Those are stored in the dns_zone
and dns_recs
tables of the psa
database.
However, I advice against querying the Plesk database directly to get any data. As the database structure might change in future updates. If you're working on any kind of integration I strongly recommend to not access the database directly, but use the Plesk REST API, XML API or Plesk CLI utilities instead. Those are the safest methods to use.