add_filter( 'posts_where' , 'func_posts_where' );
function func_posts_where( $where ) {
global $wpdb;
global $WP_Views;
if(in_array($WP_Views->current_view, array(485))){ //the ID of each "wp_view" this applies to. Multiple views, separate ID's by commas
$where = str_replace("CAST(mt1.meta_value AS SIGNED)","UNIX_TIMESTAMP(mt1.meta_value)",$where); //NOTE: 'mt1' is set by the WP View as the first filter added for a custom field. if a filter is added before the "_EventStartDate" - this will be mt2 or other...
}
return $where;
}