Hi John
I gave up in the end I used the following but it returns only a -1 in my number field. I’ll have to try again another time thanks for your help though.
`add_action(‘acf/save_post’, ‘calc_time’, 1);
function calc_time($post_id) {
$start = get_field(‘consultation_start_time’, $post_id);
$end = get_field(‘consultation_end_time’, $post_id);
// calculate difference
// see https://stackoverflow.com/questions/10557076/adding-two-time-values-of-similar-formats-using-php
$calculated_time = ($end.” -“.$start);
update_field(‘total_duration’, $calculated_time, $post_id);
}
