Meta Box

Now it's working perfectly

Thanks

Don't know if this is also related to the update (4.7.1 right now), but I just realised that I cannot insert images in post if MetaBox plugin is active! WP open the selection panel and nothing is show. Add images to post work as intended if I deactivate the plugin.
Please help

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!