Image Optimizer Schedule

Hi,

I would like to optimise unoptimized images automatically instead of manually.

Is there a function/hook/filter/action that I can place in functions.php so that I can setup a Cron job?

Though I set the setting to optimise upon upload, one of my plugins (ACF) which I use to upload image saved the uploaded image without being optimised according to the resolution and size I set.

Please help.

Thank you
Johnny