Response from the web host below – is there anything else in WordPress which could be stopping the script?
Thanks for the details. I have been able to replicate this and it does appear to time out after 29 seconds. However I have created a simple test page to test the execution time at http://catherinebargh.com/php_execution_test.php. This
simply sleeps for 40 seconds and prints out some text which is successful.
This shows that something within the application is reducing the max_execution_time to 29 seconds.
I have tried all of these solutions, but they don’t work. Even though the execution time has been set to 120 on the server, plus I installed the plugin from your link above, but the error is the same. I have asked the host what else could be forcing the 29 second error.