Not quite a bug … but there is a mistake in the api docs
When I want to change a targeted date the api docs show for date-time this:
“targeted_when”:“2023-09-08T14:15:22Z”
With the Z as last character it shows an internal server error, when I remove the Z it works perfectly.
We’ve fixed this in Supernotes 3.1.2 
Additionally, you are now allowed to use “offset-aware” datetimes in order to more easily set a time based on your local time (assuming you know the UTC-offset).
So for example if you are in UTC+8 as I am, you can set a targeted date for noon (local time) like so:
{
"targeted_when": "2024-06-12T12:00:00+08:00"
}