Create An Alarm

[Taifun]

this extension might help

[PAID] Alarm Manager Extension with Notification or Autostart

Description Alarm Manager Extension to send a notification or autostart the app at a given time or at boot time only once or repeated by interval (15 minutes, half hour, hour, half day, day and week, month and year). After clicking the notification your app will be started. You can define a start text, which will be passed to your app in method 'get plain start text' and trigger some action after your app is started. You also can define several alarms, just use a different id for each alarm. A…

and if you want to use the built in alarms see here

App Inventor Extensions: Alarm | Pura Vida Apps

Taifun