Hello,
This can be done with custom JavaScript. Here is the pseudo-code:
First step: enqueue your JS file:
add_action( 'rwmb_enqueue_scripts', function() {
wp_enqueue_script( 'your-js-id', 'url-to-your-js', ['jquery'], '', true );
} );
And in your JS file:
jQuery(function(){
var $start = $( '#start_date' ),
$end = $( '#end_date' );
$start.datepicker( {
onSelect: function( dateText ) {
$end.val( dateText );
}
} );
});
