When using the following payment methods, you can not edit the payment date yourself: Bancontact (either via the Payconiq by Bancontact app or with a banking app that supports the Bancontact functionality), Visa, Mastercard, Apple Pay ...
This is because it concerns a 'card payments'. As a third party, POM doesn't have access to the payment calendar functionality of banking apps. This feature is generally available for regular bank transfers, not for card payments.
The payment will therefore be completed immediately. You could compare it with a card payment in a store.
However, some POM clients do offer the possibility to pay on due date. If this is the case, you'll be able to execute payments a couple of days before the due date (to take into account processing time between banks), with just one click.