Large S3 content export to PDF

In our PHP app we offer the ability to export media to PDF. Most of this media is stored on S3. The idea is that a customer can select the media to export (usually pictures) and they are thrown into a single PDF document for the customer to download. We use the media in an HTML template with serves as a timeline to give to the customer. Whenever a customer tries to export a large number of pictures (say over 500) it seems that we are hitting a PHP or Laravel timeout in that the request is taking too long. I assume that the constant content download from S3 is making the request take a very long time.

Can anyone offer some suggestions on how to do this in a more efficient manner?

via Chebli Mohamed