CRON URL is available in this plugin. You have to trigger/schedule this URL from your server once every hour(Once every hour is recommended for this plugin) . Plugin will send/schedule the newsletter whenever your URL is triggered. Step-by-step tutorial on how you can setup cron task on your own server through the cPanel or Plesk available below.
How to schedule auto emails in Parallels Plesk?
How to schedule auto emails in cPanel?
Hosting doesn’t support cron jobs?
If you don’t have cPanel or Plesk account and your hosting doesn’t support cron jobs. Don’t worry, Lots of vendors available for this action. I recommend EasyCron! The easiest way to configure advanced scheduled tasks.
What is EasyCron? What service does it provide?
EasyCron is an online cron job service provider. You may register free and add cron URL of your plugin into EasyCron system, and it will trigger your cron URL at specified time or by time interval according to the setting you made.