How to avoid "The application did not respond in time" error when sending large number of emails?

Problem/Motivation

I’m using this module to send ~90 emails via webform submission.

It works to send them, but there is a long load time after pressing ‘submit’ on the form and eventually the page gives a WSOD with the error message “The application did not respond in time”
However, it actually does send the all the emails. But if you refresh the page with the error message, it will restart the sending email process.

Is there some fix for this or memory setting I can increase to let the module take more time to respond?
Thanks very much for this module.