If you want to repeat your message at a certain period of time please use the function of repeating in the scheduling settings.
Go to "Schedule settings" in the bottom of the message creation page. Click on the button to open this section.
Schedule the time when you want the notification to be sent:
Then select the "Repeat the message" line:
By default you will have the setting of repeating the message every hour (60 minutes).
Minimum: repeat the same message every hour.
Maximum: repeat the same message once in 30 days.
When the setting is done, please send your message or save it as a draft if you want to make any adjustments later (before the message is sent to subscribers).