cron - PHP output buffering not flushing -

i have ob_start(); in header.php , ob_end_flush(); include("cron.php"); in footer.

now cron.php takes few seconds load takes time page render.

how come isn't rendering considering have flushed output? know browsers mess , in past have been techniques have tried them (eg. adding flush(); or utf-8 header) none of them have worked.

is there solution works or there way me accomplish this?

how wordpress include it's cron file?

header.php:

<?php     ob_start();     require_once("config.php"); ?> 

then there's page code.

footer.php:

<?php ob_flush(); flush(); ob_end_flush(); require("cron.php"); ?>