Note 1, that will not work if php is running as a CGI with suexec.
Note 2, it is not recommended to set max execution time so high. One piece of bad php code, could lock the php processor up, even with a modest number of connections.
Note 3, default Apache Timeout directive and IIS CGI Timeout function is 300 seconds. If they are still at the default, setting max_execution_time higher than 300 will not gain you more time than the Timeout directive/function.