You can hook into post_updated action, if you want to access the post’s data after it’s been published. This hook passes the post’s ID, inundated post object, and updated post object.
add_action( 'post_updated', 'update_event_date', 10, 3 );
function update_event_date( $post_id, $post_after, $post_before ){
$post_type = get_post_type( $post_id );
$event_datee = get_post_meta( $post_id, '_EventStartDate', true );
if ( $post_type == 'tribe_events' ) {
$month = date( "m",strtotime( $event_datee ) );
update_post_meta( $post_id, 'event_month', $month );
}
}