Okay, I found some pointer from zilveer, here:
https://support.advancedcustomfields.com/forums/topic/adding-custom-javascript-to-date-and-time-picker-fields/
and also here:
https://www.advancedcustomfields.com/resources/acf-input-admin_footer/
With this result, that seems to be working!
<?
function my_acf_input_admin_footer() {
?>
<script type="text/javascript">
(function($) {
acf.add_filter('date_picker_args', function( args ){
args['onChangeMonthYear'] = function(y, m, i){
var d = i.selectedDay;
$(this).datepicker('setDate', new Date(y, m-1, d));
}
return args;
});
})(jQuery);
</script>
<?php
}
add_action('acf/input/admin_footer', 'my_acf_input_admin_footer');
?>
