date-to-title.php

<?php
    if ( empty( $_POST['acf'] ) ) {
        return;
    }

    if (
        !isset( $_POST['acf']['field_543aee78c4176'] )
        || !isset( $_POST['acf']['field_543aee84c4177'] ) )
    {
        return;
    }

    $timestamp_from = strtotime( $_POST['acf']['field_543aee78c4176'] );
    $timestamp_to = strtotime( $_POST['acf']['field_543aee84c4177'] );

    $uncertain_date = ( intval( $_POST['acf']['field_543dcf05b7eb1'] ) == 1 );

    $format = ( $uncertain_date ) ? 'F Y' : 'F j, Y';

    $from = date( $format, $timestamp_from );
    $to = date( $format, $timestamp_to );

    $y1 = date( 'Y', $timestamp_from );
    $y2 = date( 'Y', $timestamp_to );

    $dates = array( $from, $to );

    if ( $y1 == $y2 && !$uncertain_date ) {
        $from = date( 'F j', $timestamp_from );
    } else if ( $y1 == $y2 && $uncertain_date ) {
        $from = date( 'F', $timestamp_from );

        $m1 = date( 'F', $timestamp_from );
        $m2 = date( 'F', $timestamp_to );

        $dates = ( $m1 == $m2 ) ? array( $to ) : $dates;
    }


    wp_update_post( array(
        'ID'         => $post_id,
        'post_title' => implode( ' - ', $dates ),
    ) );

Are ACF field ID's such as field_543aee78c4176 constant, or does ACF ever change that internal reference?