I actually created this exact kind of reminder framework already, it resets a date/time with a future time based on a programmed interval, then shows it in the UI. Since it is a time event, you can combine with a notification automation using that time as a trigger, with conditions based on time/vacation/etc to prevent it from being shown when you do not want it to.
Since you are using a door sensor, that can be used in a second automation to trigger the reset script. Now you can see the state of the next scheduled event in the UI, reset manually, reset from the door status, and alert you through automation if you do not let them out before that time.
I also have a separate general notification and alert framework designed that would be great for this, however it is not documented in the forum yet. It is designed primarily for Kodi users, and sends a notification to the Kodi UI, the user’s phones, and optionally to the persistent notifications tab in lovelace.
I am almost ready with my new master template code which I will post in that topic.
You would need to create the helper first, such as input_datetime.dogs_out
Templated code for the UI would look something like this:
type: 'custom:decluttering-card'
template: next_event
variables:
- entity: input_datetime.dogs_out
- name: Let out the dogs
- icon: dog-side
- interval: 10800
- interval_text: Every 3 hours
The reset automation would call the reset script
service: script.script_set_timedate
service_data:
entity: input_datetime.dogs_out
timedate: 10800
The initial morning reminder would need to be an additional trigger for the notification automation, since the time/date match would occur at an earlier time when the conditions for the automation prevent the notification. If you have “wake detection” that could do it, otherwise you can set to occur at 8am every day.