How to schedule a Jenkins Job dynamically based on the time value in database
Jenkins itself isn't very good at using external data sources to drive dynamic job scheduling.  The reason for this is that job configuration, including scheduling, is built statically, either manually via the web UI, or with code via a Pipeline script which is run at job execution time.  Even if the Pipeline script builds the job configuration in a dynamic way, the configuration itself will be locked in until the next job execution.

The easiest way to have flexible build schedules is use an external source to drive your builds.  The hook mentioned in the comments would be ideal, but it sounds like that is not possible for you.  Another idea would be to have a cron job on your database server that runs once a day, grabs the build time from the database, and schedules the build for that time.  I'm sure this isn't a great solution, but it's just an example.