Ninja Notifier comes with a unique feature of being able to schedule the 'Red Alerts' messages you send to your subscribers. If you know in advance that you are having a store special or you want to send all your subscribers a conference reminder ... or anything else that you may know about in advance - you'll like want to use the Scheduled Notifications feature of Ninja Notifier. *sorry not available to the Free or Starter editions.
But before you can actually use the Scheduled Notifications feature, you'll need to setup a cron job - don't worry your web host will be able to set this up for you in a few minutes. All you have to do is give them the cron job link located on the FB/License or the Add Notification page.
Here are the settings for a cPanel setup:
And here's a quick walk-through of how we do it on our Rackspace cloud server.