Reply To: Hook on field change

• Beee

• March 22, 2018 at 10:33 pm

This should give you a nudge in the direction.
This code needs to placed in functions.php.

function acf_57448( $post_id ) {

    $start_date = get_field( 'field_name', $post_id );

    // do stuff to calculate ETA

    update_field( 'eta_field_name', $post_id )

}
add_action( 'acf/save_post', 'acf_57448', 20 );