545124 Magic Script Button + Remember which user watched the video

This is what I need. We have page with sales video. Visitor comes to out site, and sees only video, he play it. Video plays until 5minutes and then "Add to Order" button appears under video. Video keeps on playing till the end. - this is the easy part :) And if visito clicks on "ATO" button, it leads him to shopping cart and so on...but if he click on "ATO" and then decides to watch video again and click BACK button in browser, I want "ATO" button to appear from start of the video, not from 5minute mark. Can you do that? I can provide with first part of the code (hidding and apperaing at 5min mark) I need done second part of the code. I need this done ASAP. Please post your proposal..