Thank you Anh Tran, it's worked like a charm.
I didn't know about those filters
I only change your code just to avoid problems with dates when there is no date value (always return 1970-01-01)
add_filter( 'rwmb_My_date_value', function( $value )
{
if ($value != '') {
return date( 'Y-m-d', strtotime( $value ) );
};
} );
add_filter( 'rwmb_My_date_meta', function( $value )
{
if ($value != '') {
return date( 'd-m-Y', strtotime( $value ) );
};
} );
Let me know if this new code is ok or there is a better way to deal with.
Thanks again!