I have working with FCM console to send push notification and it has an option to schedule the delivery date.
But in the references, this API is not documented as an option. I need to know if its possible to push a notification with predefined delivery date through a POST request.
If you're looking for a public API of FCM for a scheduled push or a payload parameter where you can set the push date, unfortunately, there's nothing like it as of the moment.
You must implement your own App Server and implement the scheduled push yourself (also mentioned it here).