How can I change the date format of the revision list?

You can filter the output like bellow:

<?php
/**
 * @param $revision_date_author
 * @param $revision
 * @param $link
 * @return mixed
 */
function filter_wp_post_revision_title_expanded( $revision_date_author, $revision, $link ) {
    $revision = get_post( $revision );
    if ( ! $revision ) {
        return $revision;
    }

    if ( ! in_array( $revision->post_type, array( 'post', 'page', 'revision' ), true ) ) {
        return false;
    }

    $author = get_the_author_meta( 'display_name', $revision->post_author );

    //You can change format Here
    $datef = _x( 'F j, Y @ H:i:s', 'revision date format' );

    $gravatar = get_avatar( $revision->post_author, 24 );

    $date      = date_i18n( $datef, strtotime( $revision->post_modified ) );
    $edit_link = get_edit_post_link( $revision->ID );
    if ( $link && current_user_can( 'edit_post', $revision->ID ) && $edit_link ) {
        $date = "<a href="https://wordpress.stackexchange.com/questions/383349/$edit_link">$date</a>";
    }

    $revision_date_author = sprintf(
        /* translators: Post revision title. 1: Author avatar, 2: Author name, 3: Time ago, 4: Date. */
        __( '%1$s %2$s, %3$s ago (%4$s)' ),
        $gravatar,
        $author,
        human_time_diff( strtotime( $revision->post_modified_gmt ) ),
        $date
    );
    return $revision_date_author;
};

// Finally add the filter
add_filter( 'wp_post_revision_title_expanded', 'filter_wp_post_revision_title_expanded', 10, 3 );

Most of the code used in this example are taken from actual wp_post_revision_title_expanded function. read more