Scheduled Reminders Showing Notifications Way Too Early

I'd start by deleting one of the errant reminders and adding it back.

Hello joskam092,

Thank you for posting in Apple Support communities. We understand that you are wanting to stope the notification for reminders that come in 12 hours prior to the actual time and date set for the reminder. We would love to provide you support on this. 

This resource tells you how to use the reminders and gives support for notifications: Use Reminders on your iPhone, iPad, or iPod touch

This resource tells you how to use notifications for apps including reminders: Use notifications on your iPhone, iPad, and iPod touch

Thank you for allowing us to support you.

Have an awesome and productive day!

joskam092,

Thank you for getting back to us. In the first resource it talks about all day reminders and changing the time or just disabling the all day reminder notification. This will disable the notifications for reminders set as "all day reminders". We would also recommend checking the way that you have your reminders set up, because if they are set up as "all day reminders" then you may still receive notifications hours before the actual event because its set as an all day notification.

The steps to follow are located in the first section of the first resource.

Cheers!