use of register_shutdown_function

[eluser]weboap[/eluser]
another suggestion to use Simultaneuos requests as per this page :

http://www.phpied.com/simultaneuos-http-...with-curl/

and set the CURLOPT_TIMEOUT to less than 300 , after it timeout you can test the results before to store them. if the feed is ok save it, if not use the one in the cache till next cron run , then in the mean time send you a report if any failed and which one exactly.
following is some links that may help explained it better:

http://stackoverflow.com/questions/63750...st-timeout

http://stackoverflow.com/questions/50011...e-function

hope it help.