Store month in local format

Hello,

You can use the filter hook rwmb_{$field_id}_value to format the date value before saving it to the database. For example:

add_filter( 'rwmb_date_03tqmu7k17qs_value', function( $new, $field, $old, $object_id ) {
    $timestamp = strtotime( $new );
    $new = wp_date( 'd F o', $timestamp );
    return $new;
}, 99, 4 );

replace date_03tqmu7k17qs with your field date ID. Please read more on the documentation
https://docs.metabox.io/filters/rwmb-field-type-value/
https://developer.wordpress.org/reference/functions/wp_date/