Hi @dvize
Sorry, the code should have looked more like:
<?php
$tours = get_field('tours');
<?php if( is_array($tours) && in_array( 'START wages-through-ages', $tours ) ): ?>
<?php // the user has selected 'START wages-through-ages' checkbox. Do nothing ?>
<?php else: ?>
<?php // my stuff ?>
<?php endif; ?>