Question about updating the item's preview image

I just need to update my item’s preview image, i already know that it has to go through the review process. but my question is do i also need to reupload the main file and and thumbnail too? or i can just leave them empty?


I’m also wondering how long it takes…

Thumbnail: 80x80px any image or design format .jpg or .png
Theme Preview Images for preview item design psd save format as jpg or png with size 590px x 300px, not forgot save image preview as 01_preview, 02_preview etc.
Main File Files for buyer (if you make html but file html, css, js no use images for buyer but use placeholder color gray background.

good luck